Fix log_type errorlog: should behave like other log handlers

[znerol]

Configuration with 'log_type' => 'errorlog' are affected by #33313. This is due to the fact that the ErrorLog handler currently doesn't correctly implement the write() method. According to other implementations, the $message parameter can be either a string or an array.

Other implementations use logDetailsAsJSON to convert a structured log message into a string. ErrorLog should do the same.

Note: This PR also removes the $tag instance variable. A log tag is important for writers like syslog and systemd where log messages of multiple subsystems are merged into a common journal. This is clearly not the case for the errlog writer.

[k-popov]

Is there any activity on having this patch accepted?
IMO this patch is important as running NextCloud in kubernetes ofter implies logging to STDERR (with later collection to Kibana). And currently the entire logging to errorlog is broken, images are required to be rebuilt with local patches applied.

[ChristophWurst]

I coincidentally submit a very similar PR at #35614.

Let's take this one. But please revive the $tag constructor arg.

[znerol]

Let's take this one. But please revive the $tag constructor arg.

If $tag needs to remain, then yours is already there.

[ChristophWurst]

Then let's continue in #35614. Mind giving the other PR a review? :)