[v9.5.x] Alerting: Fix state manager to not keep datasource_uid and ref_id labels in state after Error

[grafana-delivery-bot]

Backport 78fc3bc from #72216

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What is this feature?
This PR fixes a bug in the state manager that is described in #71467. It updates the state manager to clean up the labels sneaked after the cacheID was calculated. I added safety to remove only if the result does not contain these labels.

This is a temporary change to remediate the problem and will be changed in #68142

Before

before-no-sound.mp4

After

after-no-sound.mp4

Why do we need this feature?
This happens only in the case when the result does not have any labels, usually when the rule uses the classic condition. The normal evaluation uses labels from the rule only. When an error happens, the error result does not have labels either, and therefore it is matched to the normal state instead of being a new state (in multi-dimensional alerts when each normal result contains labels). The state manager adds extra labels after the state identifier is calculated. Therefore, this makes the normal result match the state that contains the extra labels, and therefore the extra labels (datasource_uid and ref_id) never go away from the state.

Who is this feature for?
Those who use classic condition and execution of Error as an error.

Which issue(s) does this PR fix?:
Fixes #71467

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.