tests: fix describe topics w/ docs and types

[NyaliaLui]

Cover letter

This test was failing because of poor STDOUT parsing that assumed a fixed number of lines. This commit removes those assumptions and uses regular expressions to parse STDOUT instead of string.split()

Fixes #7851

Changes from force-push 81ce31c:

• Yank out the line for redpanda.datapolicy from the property table and check it on its own
• Parse output until we reach the end of the property table. Then parse the documentation section
• name in properties.keys() can be rewritten as name in properties
• Check the documentation section using indexes instead of an iterator

Changes from force-push 24792e4:

• For redpanda.datapolicy, check for default_config is sufficient
• Use for line in output instead of an iterator so the StopIterator is automatically handled

Changes from force-push b80b818 and b11b7d8:

• Use enumerate to find the index of the table separator line
• Assert that the docs section is there

Backports Required

• none - not a bug fix
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v22.3.x
• v22.2.x
• v22.1.x

UX Changes

• none

Release Notes

• none

[graphcareful]

Huge improvements, left two small comments, nice work!

[graphcareful]

LGTM

[NyaliaLui]

CI failure is #7874 which should be fixed upstream now

I'm restarting the K8s-operator and golinter

[dotnwat]

lgtm.

@NyaliaLui for the future: we control the wrappers around clients (e.g. KCL) so we can add the sort of parsing you are doing in this test to the client wrapper itself so that other users of the client don't accidentally recreate all the parsing later on.