rpk: group describe supporting regex

[daisukebe]

Motivation explained in #17710

when redpanda admins/support want to get a description of all consumer groups...
the drill is a  "for i in " loop based on "rpk group list" ..
which runs
rpk group describe $i
on each group

We should have the ability to get the group description in a single rpk group command

I lean towards supporting regex in the describe command as topic describe does. As group describe already accepts more than one group in one command, I feel it is natural to support regex too.

Fixes #17710

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v24.1.x
• v23.3.x
• v23.2.x

Release Notes

Improvements

• rpk: group describe supports --regex flag

[r-vasquez]

LGTM, just 2 requests but thanks for doing this!

[daisukebe]

Based on @r-vasquez 's feedback, made some changes below and rebased.

• moved examples to the cobra.Command's Example field
• made the regex function universal under the utils package, regex_filter.go
• removed the regex logic from topic/utils.go
• moved the test code from topic/utils_test.go to utils/regex_filter_test.go

[r-vasquez]

This is awesome, thanks!

[daisukebe]

/ci-repeat 3

[daisukebe]

@r-vasquez , is the build failure relevant?

[r-vasquez]

@daisukebe They were unrelated failures, not sure why the bot didn't retry (I did it manually). Merging it now, thanks

[vbotbuildovich]

/backport v24.1.x

[vbotbuildovich]

/backport v23.3.x