release-21.2: log: add support for decoding JSON logs

[dhartunian]

Backport 1/1 commits from #79356.

/cc @cockroachdb/release

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Previously, our logging code did not have the ability to recognize and
decode JSON formatted log files. This led to problems when retrieving
logs via API endpoints and when running commands such as merge-logs to
process logs from debug.zip files.

This commit adds support for the json, json-compact, json-fluent, and
json-fluent-compact formats via one generalized JSON decoder.

Resolves #66684

Release note (ops change, cli change): debug zip and merge-logs commands
will now work with JSON formatted logs.

Jira issue: CRDB-14742

Release justification: high-need log management change that's additive to existing log parsing

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[abarganier]

Looks good, aside from one detail that I wasn't sure about.

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @abarganier and @dhartunian)

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pkg/util/log/log_decoder.go line 140 at r1 (raw file):

		return "crdb-v2", nil
	}

Do we want a match against v1IndicatorRE here as well? I noticed that it's done in the original PR.

[dhartunian]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @abarganier)

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pkg/util/log/log_decoder.go line 140 at r1 (raw file):

Previously, abarganier (Alex Barganier) wrote…

Do we want a match against v1IndicatorRE here as well? I noticed that it's done in the original PR.

fixed. good catch. must have gotten lost in the merge conflict resolution.

[abarganier]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @abarganier)

[dhartunian]

Realized the test failures and merge confusion was because there's a prior backport missing: #83748

will wait for that to merge.