azurerm_storage_container_immutability_policy - Fix immutability_period_in_days validation

[abicky]

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Description

This PR fixes #28660 and supports the feature to extend a locked immutable policy.
As described on https://learn.microsoft.com/en-us/azure/storage/blobs/immutable-storage-overview#locked-versus-unlocked-policies, we can increase immutability_period_in_days five times.

A maximum of five increases to the effective retention period is allowed over the lifetime of a locked policy that is defined at the container level.

PR Checklist

• I have followed the guidelines in our Contributing Documentation.
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Changes to existing Resource / Data Source

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Testing

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Here is the output of TestAccStorageContainerImmutabilityPolicy_completeLocked with debug logs when I ran the test after deleting the line t.Skip("this test for manual execution only"):
https://gist.github.com/abicky/7c4559ca31fc4ee11113ab5b6b8f72fb

Change Log

Below please provide what should go into the changelog (if anything) conforming to the Changelog Format documented here.

• azurerm_storage_container_immutability_policy - fix immutability_period_in_days validation

This is a (please select all that apply):

• Bug Fix
• New Feature (ie adding a service, resource, or data source)
• Enhancement
• Breaking Change

Related Issue(s)

Fixes #28660

Note

If this PR changes meaningfully during the course of review please update the title and description as required.

[abicky]

I've only added the condition for when the policy is locked, so you can more easily understand the changes on https://github.com/hashicorp/terraform-provider-azurerm/pull/28661/files?w=1.