Add profile image synchronization

[SanseroGames]

This PR addresses #85 and implements profile image synchronization from LDAP to Jellyfin.

The profile image is set when a user account is created and automatically synchronized in a configurable interval using a scheduled task. The attribute to retrieve the profile image can be configured and is set to jpegphoto by default. Profile image synchronization is disabled by default and can be enabled in the settings.

The profile image is only changed if it has been changed in LDAP. To detect the change a hash of the image is stored in the plugin configuration for the user and compared to the hash of the LDAP attribute when the scheduled task is run.

This PR has been tested with an LLDAP instance as LDAP-backend, but other LDAP servers should behave the same.

[crobibero]

Just a quick review from my phone. Will review scheduled task and sync changes in coming days

[SanseroGames]

Is there anything else you need me to do? Should I squash the commits?

[nerddotdad]

I'm hoping to understand what format we should have in the jpegPhoto field? should it be a url? Should it be a base64 hash? I've been testing and I can't seem to get it to populate that field in the users config section either way. Looks like a few people are struggling to understand the expectations of that field #163

[nerddotdad]

@SanseroGames were you able to get this functioning after deploying? If so are you willing to offer a bit of insight into what the contents of the jpegPhoto ldap field need to be? It seems folks are getting hung up on it and from what I can tell it seems like the plugin essentially writes the contents of the ldap field into a file named profile.jpg. I think the hope is that it could either take a URL of an image or a base64 string in that field so it could be decoded by the plugin.

Any assistance would be great!