[WIP] Update null TenantId implementation for tenant-agnostic entities

[Copilot]

Thanks for the feedback on #7226. I've created this new PR, which merges into #7226, to address your comment. I will work on the changes and keep this PR's description up to date as I make progress.

Original PR: #7226
Triggering review: #7226 (comment)

@copilot open a new pull request to apply changes based on this feedback

However, be careful that we still remove stale descriptors when eg. workflow definitions are removed, after which we refresh the registry of descriptors, which may no longer "see" the delete workflow definition, therefore its descriptor becoming stale. There is at lest on component test that guards against this, so make sure to run them whenever you make a change here.

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[Copilot]

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