Support logging the impersonator user, if any

[ste93cry]

Fixes #642 by logging the impersonator user as part of the metadata of the User Interface. @hunhejj given that you asked for this feature, would you mind trying this out and see if it works?

[hunhejj]

I tried to test it on our project @ste93cry but unfortunately I get way too many conflicts when trying to install the branch directly.

[hunhejj]

Btw. in your original thread you suggested using a dedicated tag but I see in the implementation that you ended up with user meta. Out of curiosity what is the advantage of it @ste93cry ?

[ste93cry]

you suggested using a dedicated tag but I see in the implementation that you ended up with user meta

Right, I didn't check at that time and I though that the user was logged as a tag, but actually there is a specific User Interface provided by Sentry to store the user information that we were already using. From the UI's perspective, the only difference is that the impersonator user is shown in the section dedicated to the user details instead of the section of the tags. However, it looks like all the extra fields that belongs to that Interface are not indexed and so aren't searchable. I think that for consistency purposes and also because "it feels more appropriate" we should keep going this way, but, as a side note, I would support the idea of asking Sentry if it was possible to make searchable all the extra fields of the user.