feat: support `slog.Group` function

[romanchechyotkin]

Added support for slog.Group

Since it has pairs to check, i decided to add func log/slog.Group to list of slog functions to make it checkable)

[romanchechyotkin]

@tmzane i will be pleased to get any feedback

[tmzane]

Thanks for the PR!

I'm not sure it's safe to just add slog.Group to the list: it doesn't have the alternative function with the context (so it should not be checked for context-only), it doesn't have the message argument (so it should not be checked for static-msg), probably something else. I'll do some research and update your PR.

[romanchechyotkin]

let me know any updates