Add custom merge function for child logger default metadata

[FoxxMD]

• Add a parameter to logger.child that accepts a function whose result will be used as the infoClone for that child
• Provide the current merge functionality as the default argument for this parameter

New PR from suggested changes in #1885

This enables a user to implement their own, arbitrary merge functionality for child loggers.

[wbt]

This seems related to a collection of related issues centered on #2029, which @maverick1872 is taking the lead on collating.

[FoxxMD]

Sure is..and I was willing to wait until that main issue was resolved before making a PR but maverick said it was unrelated so here we are 🤷

[wbt]

@FoxxMD Sorry for not reading up on the whole chain! I was mainly adding the comment here to make sure that he'd see it. The strategy appears to have been successful.

[maverick1872]

@FoxxMD I've looked over this implementation and it makes sense to me. I'd like to see test included of course if we were to accept this change. That being said my overarching thought is that a more appropriate implementation would be allowing end users to extend the Logger class itself. There is currently an open issue for this and I believe it would allow for the same functionality, albeit in a different format.

@wbt Do you have any opinions on this or my perspective?

[wbt]

@maverick1872 No strong informed opinions here; I'm deferring to you for in-depth evaluation.

[FoxxMD]

@maverick1872 extending the class would work fine for me if it solves the same issue 👍 I would also be happy to rebase my PR and get it to pass these tests if you'd like to have this PR as an option, just in case. Your call.

[maverick1872]

@FoxxMD I'm going to remove this from #2029 as it's not intended to solve the underlying merging of metadata issue. I think long term having a base class (#1902) that can be extended as people see fit is our most ideal solution. I'd like to get the other members opinions on this though before making a hard call on this.

@wbt @fearphage @DABH