loki.process Add stage.pattern to use LogQL pattern parser to extract values

[rowanmoul]

Request

It would be great if there was a stage.pattern stage for loki.process. It would function similarly to stage.regex, except use the pattern syntax instead. Given that stage.match already uses LogQL, I imagine the necesary dependencies already exist in the alloy codebase.

Use case

The pattern syntax is much easier to read and understand, reducing the chance of mistakes. The docs also claim it is faster/more efficient than regex.