Set IMDSv2 as optional

[wyike]

What type of PR is this?
/kind bug

What this PR does / why we need it:
IMDSv2 enablement in #4037 is a breaking change. We need give customer time to migrate their applications.

This PR set IMDSv2 as optional as the default to not break existing customers. The instance will be the same instance metadata options as before after capa upgraded:

        httpPutResponseHopLimit: 1
        httpTokens: optional

Customer can still customize instance metadata option themselves by configuring in the awsmachinetemplate/instanceMetadataOptions.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #4275

Special notes for your reviewer:
In future, if we want to enable IMDSv2 as default, we switch to below default values:

        httpPutResponseHopLimit: 2
        httpTokens: required

Checklist:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

Release note:

Defaults to configure instance metadata with IMDSv2 optional

[wyike]

/test pull-cluster-api-provider-aws-e2e

[wyike]

/test pull-cluster-api-provider-aws-e2e

[Skarlso]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Skarlso

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[wyike]

/cherry-pick release-2.1

[k8s-infra-cherrypick-robot]

@wyike: #4274 failed to apply on top of branch "release-2.1":

Applying: Default IMDSv2 to optional
.git/rebase-apply/patch:222: trailing whitespace.
Before you decide to use IMDSv2 for the cluster instances, please make sure all your applications are compatible to IMDSv2. 
warning: 1 line adds whitespace errors.
Using index info to reconstruct a base tree...
M	api/v1beta2/awsmachinetemplate_webhook_test.go
M	api/v1beta2/types.go
M	controllers/awsmachine_controller_unit_test.go
M	docs/book/src/topics/instance-metadata.md
Falling back to patching base and 3-way merge...
Auto-merging docs/book/src/topics/instance-metadata.md
CONFLICT (content): Merge conflict in docs/book/src/topics/instance-metadata.md
Auto-merging controllers/awsmachine_controller_unit_test.go
CONFLICT (content): Merge conflict in controllers/awsmachine_controller_unit_test.go
Auto-merging api/v1beta2/types.go
Auto-merging api/v1beta2/awsmachinetemplate_webhook_test.go
CONFLICT (content): Merge conflict in api/v1beta2/awsmachinetemplate_webhook_test.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Default IMDSv2 to optional
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherry-pick release-2.1

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[wyike]

/cherry-pick release-2.1

[k8s-infra-cherrypick-robot]

@wyike: new pull request created: #4281

In response to this:

/cherry-pick release-2.1

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.