fix: fix access policy and assignment on redis as only one can be configured at a time

[josh-barker]

Uses locks to prevent multiple resources trying to update the same redis cache in parallel, because Redis will error saying that another job is in progress.

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Change Log

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• azurerm_redis_cache_access_policy - fix error when configuration occurs in parallel [fix: fix access policy and assignment on redis as only one can be configured at a time #26085]
• azurerm_redis_cache_access_policy_assignment - fix error when configuration occurs in parallel [fix: fix access policy and assignment on redis as only one can be configured at a time #26085]

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)

Closes #25802

Note

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

[stephybun]

Thanks @josh-barker LGTM 👍

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