Set current project/group in WebHookWorker context [RUN AS-IF-FOSS]

What does this MR do?

Currently this isn't always reliably detected, depending on how the worker is triggered.

By setting this explicitly we always see the related project and namespace in Kibana, and also the subscription plan in EE.

This also sets the related_class field to the webhook type, which is useful for troubleshooting purposes.

Part of #330133 (closed), this will help with determining suitable thresholds for webhook rate-limiting.

Does this MR meet the acceptance criteria?

Conformity

• [-] I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• [-] I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• [-] I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• [-] I have tested this MR in all supported browsers, or it's not needed.
• [-] I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.