Drop stale metrics cache

[tyrken]

What this PR does

Works around the old incomplete cached items breaking metrics collection. Not the cleanest solution but it seems to work.

Which issue(s) this PR closes

Closes #4455

Checklist

• [ ] Unit, integration, and e2e (if applicable) tests updated
• [ ] Documentation added (or pr:no public docs PR label added if not required)
• [ ] Added the relevant release notes label (see labels prefixed w/ release:). These labels dictate how your PR will show up in the autogenerated release notes.

Notes

If this PR takes a while to merge & you can't build a custom image yourself, you probably can achieve the same effect by dropping the below keys from your installation's cache store, e.g. Redis if following the suggested setup.

• oncall_alert_groups_total_1
• oncall_alert_groups_response_time_seconds_1

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

:white_check_mark: Ferril
:x: tyrken
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[joeyorlando]

@Ferril does this close https://github.com/grafana/oncall/issues/4455?

[Ferril]

@Ferril does this close #4455?

yes

[Ferril]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.1 out of 2 committers have signed the CLA.✅ Ferril❌ tyrkenYou have signed the CLA already but the status is still pending? Let us recheck it.

Hi @tyrken 👋 Could you please sign this agreement, so I can merge your PR?

[Ferril]

created a new PR - https://github.com/grafana/oncall/pull/4695, close this one