Access request actor in error handler

[SychO9]

Fixes #1847

Changes proposed in this pull request:
Very well explained here: #1847 (comment)

Reviewers should focus on:
With this, the actor can be accessed through $request->getAttribute('actorReference')->getActor()
Do we want to deprecate $request->getAttribute('actor') ? If so do we want to replace it with the above everywhere as well or leave that for #869 ?

Confirmed

• Backend changes: tests are green (run composer test).

[askvortsov1]

To be honest, I would prefer to see #869 happen first; that way we can start by abstracting away access, then switch up the underlying implementation. That being said, I'd lean towards not switching anything up yet, and only deprecating the old way after we abstract it away through RequestUtil.

[SychO9]

Sounds good, we can come back to this after #869 is implemented.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. We do this to keep the amount of open issues to a manageable minimum.
In any case, thanks for taking an interest in this software and contributing by opening the issue in the first place!

[askvortsov1]

This is from half a year ago???? How time flies... Anyways, this can be updated now that #2449 has been merged.

[askvortsov1]

Do we want to deprecate $request->getAttribute('actor') ?

I would be in favor of deprecating it, and leaving it for now.