Allow adding effect's contextual environment to the log context

[iRevive]

Closes https://github.com/typelevel/log4cats/issues/461. Some ideas are based on #676.

[iRevive]

I made log4cats-mtl module.

Should I set an upcoming release via tlVersionIntroduced := List("2.12", "2.13", "3").map(_ -> "2.7.0").toMap to suppress MiMa errors in the module? Or should I bump the base version instead: tlBaseVersion := 2.7?

[armanbilge]

If we are making a log4cats-mtl module, we should consider that cats-mtl may become a direct dependency of Cats Effect via https://github.com/typelevel/cats-effect/issues/3385. Although that might be Cats Effect core only, and not the std module we're using here.

Just want to make sure that we think about the migration path in the case MTL ends up on the log4cats-core classpath (an acceptable migration path may be to accept the less-than-ideal situation as a historical artifact :)

[iRevive]

Is there any ETA? It would be nice to have Local as a part of cats-effect.

[armanbilge]

It could be as early as Cats Effect 3.6. I think last time that we discussed it Daniel was pretty convinced.