Add audit logs for ai_workflows actions

What does this MR do and why?

Adds audit logs for any API requests which were authenticated using a token with ai_workflows scope. Audit log is created no matter if request was successful or not (even if request fails later after authentication for any reason) - IOW we log any API request attempts done with the token.

References

Related to #499461 (closed)

MR acceptance checklist

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Screenshots or screen recordings

How to set up and validate locally

There are two options:

• Either setup and use Duo Workflow locally (instructions in https://docs.gitlab.com/ee/development/duo_workflow/), then run a workflow and check events in audit log
• Update scopes for an existing token - set only ai_workflows scope for the token (this scope is used also by Duo Workflow) - this can be done in console with PersonalAccessToken.find(22).update_column(:scopes, ["ai_workflows"]). Then run any API request for which token with this scope is allowed, for example: curl --header "PRIVATE-TOKEN: <token>" "http://192.168.1.8:3000/api/v4/projects/1/issues/3"