Update storage account naming convention to use subscription IDs as a unique string seed

[glennmusa]

Description

This change adds to the implementation from #558 to use the relative subscription ID as a uniqueString() seed to reduce likelihood of storage account collisions.

While not a full proof solution to unqiueness, since Subscription IDs are GUIDs this should generate a hash unique to the deployment subscriptions and prevent naming collisions with deployments to other subscriptions while preserving a redeployment into the same subscription + resourcePrefix and resourceSuffix pair.

It's likely that multiple users deploying into the same subscriptions will collaborate.

It's unlikely that if I pull MissionLZ from the wild I'll have any idea of what other users around the world have named their resourcePrefix and resourceSuffix.

Today

Today, in the event someone picks a "unique" resourcePrefix and "unique" resourceSuffix pair that's already been used, when the storage account name is calculated they'll get a storage account name collision:

missionlz/src/bicep/mlz.bicep

Line 477 in d2441cb

var storageAccountNamingConvention = toLower('${resourcePrefix}st${nameToken}${uniqueString(resourcePrefix, resourceSuffix)}') // we use uniqueString() here to generate uniqueness

Proposed changes

This change proposes passing the relative subscription ID for the hub/spoke that the storage account is being created within as another seed for determining the uniqueString() hash:

First, it creates the token for replacement unique_storage_token:

missionlz/src/bicep/mlz.bicep

Line 482 in e5fbc84

var storageAccountNamingConvention = toLower('${resourcePrefix}st${nameToken}unique_storage_token')

Then, each hub/spoke generates the name with token replacement:

missionlz/src/bicep/mlz.bicep

Lines 492 to 494 in e5fbc84

	var hubLogStorageAccountShortName = replace(storageAccountNamingConvention, nameToken, hubShortName)
	var hubLogStorageAccountUniqueName = replace(hubLogStorageAccountShortName, 'unique_storage_token', uniqueString(resourcePrefix, resourceSuffix, hubSubscriptionId))
	var hubLogStorageAccountName = take(hubLogStorageAccountUniqueName, 23)

Issue reference

The issue this PR will close: #556

Checklist

Please make sure you've completed the relevant tasks for this PR out of the following list:

• All acceptance criteria in the backlog item are met
• The documentation is updated to cover any new or changed features
• Manual tests have passed
• Relevant issues are linked to this PR

[brooke-hamilton]

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