enhancement(sources): add a runtime-swappable TLS acceptor to TCP sources

[guilload]

Summary

Add a runtime-swappable TLS acceptor so a TCP source can pick up rotated
certificate material without rebinding its listener.

• TlsAcceptorReloader holds the served acceptor behind
  an Arc<ArcSwap<SslAcceptor>>; reload() rebuilds it via
  TlsSettings::acceptor() and swaps it in. WeakTlsAcceptorReloader
  (from downgrade()) is what a background reload task holds, and reports
  once the listener is gone so the task can stop.

• MaybeTlsSettings gains reloadable_acceptor() and bind_reloadable().
  The listener now snapshots the current acceptor on each accept(), so a
  reload only affects connections accepted afterwards; in-flight connections
  keep what they negotiated. bind()/bind_with_allowlist() delegate, so
  existing behaviour is unchanged.

• TcpSource::run and try_bind_tcp_listener take an
  Option<TlsAcceptorReloader>; all in-tree callers pass None, so no
  existing source changes behaviour.

Also bump openssl from 0.10.80 to 0.10.81 and replace the deprecated Asn1StringRef::as_utf8 with to_string.

Vector configuration

How did you test this PR?

Tested locally with OPW, Splunk TCP source, and cert reloader similarly to unit test in tls::reload.

Change Type

• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

Notes

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[datadog-vectordotdev]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 7893659 | Docs | Give us feedback!}

[chatgpt-codex-connector]

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[thomasqueirozb]

@codex review

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[bruceg]

LGTM. TBH I did a double take at seeing the Arc-in-Arc regime of Arc<ArcSwap<T>> but it eventually made sense.

[thomasqueirozb]

/ci-run-regression origin/master