Query Keycloak for user deletions every 5 minutes

[eleftherias]

Summary

Change the interval that we use to poll Keycloak for deletion events, from 1 hour to 5 minutes.
This way, if a user deletes their account elsewhere, they can re-create their account on Minder after at most 5 minutes.

Fixes #4614

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• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

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Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[blkt]

question (non-blocking): just a clarification: this is unrelated, right?

[eleftherias]

It is unrelated to the interval, but I figured if we're querying every 5 minutes, then we want to cancel any old event processing if it's taken longer than 5 minutes, to avoid attempting the same deletions twice.

[evankanderson]

There was another timeout on line 149; I'll send a PR for it.

[coveralls]

coverage: 53.109% (+0.004%) from 53.105%
when pulling f00399d on eleftherias:4614-delete-user-interval
into 6514ae4 on stacklok:main.