add silence alarms for hmpps-domain-services-preproduction and -test lb alarms

[robertsweetman]

A reference to the issue / Description of it

Instances are turned off on a schedule so these LB endpoint alarms keep firing

How does this PR fix the problem?

Set's pagerduty to 'silence' them on a schedule (daily overnite and over the weekend)

How has this been tested?

Please describe the tests that you ran and provide instructions to reproduce.

Same type of code is working elsewhere (CSR trainab instances)

Deployment Plan / Instructions

Will this deployment impact the platform and / or services on it?

Nope

Checklist (check x in [ ] of list items)

• I have performed a self-review of my own code
• All checks have passed
• I have made corresponding changes to the documentation
• Plan and discussed how it should be deployed to PROD (If needed)

Additional comments (if any)

{Please write here}

[github-actions]

Trivy Scan Success

Show Output

```hcl

---

Trivy will check the following folders:
terraform/pagerduty

---

Running Trivy in terraform/pagerduty
2024-09-20T11:39:43Z INFO [db] Need to update DB
2024-09-20T11:39:43Z INFO [db] Downloading DB... repository="ghcr.io/aquasecurity/trivy-db:2"
2024-09-20T11:39:45Z INFO [vuln] Vulnerability scanning is enabled
2024-09-20T11:39:45Z INFO [misconfig] Misconfiguration scanning is enabled
2024-09-20T11:39:45Z INFO Need to update the built-in policies
2024-09-20T11:39:45Z INFO Downloading the built-in policies...
74.86 KiB / 74.86 KiB [-----------------------------------------------------------] 100.00% ? p/s 0s2024-09-20T11:39:45Z INFO [secret] Secret scanning is enabled
2024-09-20T11:39:45Z INFO [secret] If your scanning is slow, please try '--scanners vuln' to disable secret scanning
2024-09-20T11:39:45Z INFO [secret] Please see also https://aquasecurity.github.io/trivy/v0.55/docs/scanner/secret#recommendation for faster secret detection
2024-09-20T11:39:46Z INFO [terraform scanner] Scanning root module file_path="."
2024-09-20T11:39:46Z WARN [terraform parser] Variable values was not found in the environment or variable files. Evaluating may not work correctly. module="root" variables="pagerduty_token, pagerduty_user_token"
2024-09-20T11:39:46Z ERROR [terraform evaluator] Failed to expand block. Invalid "for-each" argument. Must be known and iterable. block="pagerduty_team_membership.modernisation_platform_membership" value="cty.NilVal"
2024-09-20T11:39:46Z INFO [terraform executor] Ignore finding rule="aws-ssm-secret-use-customer-key" range="aws.tf:5-16"
2024-09-20T11:39:46Z INFO [terraform executor] Ignore finding rule="aws-ssm-secret-use-customer-key" range="aws.tf:102-111"
2024-09-20T11:39:46Z INFO [terraform executor] Ignore finding rule="aws-ssm-secret-use-customer-key" range="aws.tf:116-125"
2024-09-20T11:39:46Z INFO Number of language-specific files num=0
2024-09-20T11:39:46Z INFO Detected config files num=3
trivy_exitcode=0

</details> #### `Checkov Scan` Success
<details><summary>Show Output</summary>

```hcl

*****************************

Checkov will check the following folders:
terraform/pagerduty

*****************************

Running Checkov in terraform/pagerduty
Excluding the following checks: CKV_GIT_1,CKV_AWS_126,CKV2_AWS_38,CKV2_AWS_39
terraform scan results:

Passed checks: 28, Failed checks: 0, Skipped checks: 10


checkov_exitcode=0

CTFLint Scan Success

Show Output

*****************************

Setting default tflint config...
Running tflint --init...
Installing "terraform" plugin...
Installed "terraform" (source: github.com/terraform-linters/tflint-ruleset-terraform, version: 0.9.1)
tflint will check the following folders:
terraform/pagerduty

*****************************

Running tflint in terraform/pagerduty
Excluding the following checks: terraform_unused_declarations
tflint_exitcode=0

Trivy Scan Success

Show Output

*****************************

Trivy will check the following folders:
terraform/pagerduty

*****************************

Running Trivy in terraform/pagerduty
2024-09-20T11:39:43Z	INFO	[db] Need to update DB
2024-09-20T11:39:43Z	INFO	[db] Downloading DB...	repository="ghcr.io/aquasecurity/trivy-db:2"
2024-09-20T11:39:45Z	INFO	[vuln] Vulnerability scanning is enabled
2024-09-20T11:39:45Z	INFO	[misconfig] Misconfiguration scanning is enabled
2024-09-20T11:39:45Z	INFO	Need to update the built-in policies
2024-09-20T11:39:45Z	INFO	Downloading the built-in policies...
74.86 KiB / 74.86 KiB [-----------------------------------------------------------] 100.00% ? p/s 0s2024-09-20T11:39:45Z	INFO	[secret] Secret scanning is enabled
2024-09-20T11:39:45Z	INFO	[secret] If your scanning is slow, please try '--scanners vuln' to disable secret scanning
2024-09-20T11:39:45Z	INFO	[secret] Please see also https://aquasecurity.github.io/trivy/v0.55/docs/scanner/secret#recommendation for faster secret detection
2024-09-20T11:39:46Z	INFO	[terraform scanner] Scanning root module	file_path="."
2024-09-20T11:39:46Z	WARN	[terraform parser] Variable values was not found in the environment or variable files. Evaluating may not work correctly.	module="root" variables="pagerduty_token, pagerduty_user_token"
2024-09-20T11:39:46Z	ERROR	[terraform evaluator] Failed to expand block. Invalid "for-each" argument. Must be known and iterable.	block="pagerduty_team_membership.modernisation_platform_membership" value="cty.NilVal"
2024-09-20T11:39:46Z	INFO	[terraform executor] Ignore finding	rule="aws-ssm-secret-use-customer-key" range="aws.tf:5-16"
2024-09-20T11:39:46Z	INFO	[terraform executor] Ignore finding	rule="aws-ssm-secret-use-customer-key" range="aws.tf:102-111"
2024-09-20T11:39:46Z	INFO	[terraform executor] Ignore finding	rule="aws-ssm-secret-use-customer-key" range="aws.tf:116-125"
2024-09-20T11:39:46Z	INFO	Number of language-specific files	num=0
2024-09-20T11:39:46Z	INFO	Detected config files	num=3
trivy_exitcode=0