Audit label creation, update and destroy events

We should track when labels get created, edited and destroyed. Sometimes it's useful for debugging or for other purposes.

From internal thread: https://gitlab.slack.com/archives/C0AR2KW4B/p1686556471361579 (valid for 90 days)

Plan

• Add audit events when adding, deleting or updating group and project labels.
• Add audit event definitions for these three new actions.
• Guidelines to do so are: https://docs.gitlab.com/ee/development/audit_event_guide/

Wider "where did this extra label come from?" strategy

1. labels are auto-created and maybe they shouldn't be 👉 #415036 (comment 1649485189) 👉 new issue Allow disabling of "auto create label if none e... (#433955)
2. it's not possible to tell who created a label 👉 #415036 (comment 1649485189) (maybe if it's within the last 7 days via logs) 👉 this issue
3. Labels can be modified by anyone in the group, maybe they shouldn't be 👉 #415036 (comment 1678554192) 👉 Introduce role-based permissions for labels (#433961)
4. Clearly show the impact of destroying a label 👉 Add label deletion confirmation and affected it... (#466606)