Add alert group state actions

[Genmin]

Summary

• add AlertGroupService methods for acknowledge, unacknowledge, resolve, and unresolve
• route each method to the documented Grafana OnCall alert group action endpoint
• cover all state-action endpoints, including escaped alert group IDs

Validation

• /opt/homebrew/bin/go test ./... -run '^Test(AlertGroupStateActions|GetAlertGroup|GetAlertGroupWithSpecialCharacters)$'\n- git diff --check\n\nNote: a full /opt/homebrew/bin/go test ./... run still fails in pre-existing integration fixture comparisons around dynamic_labels in integration_test.go; the alert group tests pass.

[cla-assistant]

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[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[the-it]

this is looking good. We need a CLA signing from you tho.