release-22.2: ccl/sqlproxyccl: add PROXY protocol support via CLI flag to sqlproxy

[jaylim-crl]

Backport commits from #99429 and #100288.

/cc @cockroachdb/release

---

This commit adds a new require-proxy-protocol flag to mt start-proxy, and
that changes the sqlproxy's behavior to support the PROXY protocol. When the
flag is set, the protocol will be enforced on the SQL listener, and supported
on a best-effort basis on the HTTP listener. If the PROXY protocol isn't used,
but is enforced, the connection will be rejected. The rationale behind doing
best-effort basis on the HTTP listener is that some healthcheck systems don't
support the protocol.

This work is needed for the AWS PrivateLink work in CockroachCloud, which
requires the use of the PROXY protocol.

Release note: None

Epic: none

Release justification: SQL Proxy change only. Changes are needed for the AWS
PrivateLink work in CockroachCloud. Doing this for 22.2 helps with rolling out
the changes.

[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 

[jaylim-crl]

Note that this PR wasn't a clean cherry-pick, especially for the first commit, as there were some CLI refactor changes that weren't backported into 22.2.

[jaylim-crl]

I'm going to close this. We'll just make this available via v23.1 for now. If there's a strong need, we can bring this back.