Add SRV DNS record support to HTTP Operator

[gtxu]

This pull request allows an HTTP connection resolve its target host and port from a DNS SRV record instead of a fixed host/port, so it can talk to services published via SRV-based service discovery(ie. AWS Service Discovery for ECS).

This changes introduces dnspython as an optional dependency to keep the core HTTP provider lightweight. To prevent DNS query flooding, a TTL cache mechanism is implemented.

• Implemented soft dependency via the srv extra.

• Built RFC 2782 compliant failover (lowest priority tier filtering and random target selection).

• Added concurrency-safe TTL caching (srv_cache_ttl) using asyncio.Lock to prevent cache stampedes in asynchronous contexts.

• Exposed srv_lookup and srv_cache_ttl configuration directly in the Airflow Connection UI via custom form widgets.

closes: #9186

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Was generative AI tooling used to co-author this PR?

• Yes - Claude Sonnet 5

Generated-by: Claude Sonnet 5 following the guidelines

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[aaron-y-chen]

Thanks for the PR 🙂

[omkar-foss]

PR looks good to me overall. Newly added tests are looking well-covered, would be nice if someone could initiate the ci checks in this PR so we can see them run and pass.

PS: I'm not a maintainer, my review is non-binding. Just trying to help out :)

[gtxu]

Found out the root cause CI failures (3/3 runs) targeting TestHttpAsyncHookSrvLookup::test_run_resolves_srv_record.
The test was failing with a real network query (dns.resolver.NoAnswer), bypassing the mock, yet consistently passing in local environments.

In Python 3.10(CI Env), mock.patch uses _dot_lookup (which calls getattr), meaning it successfully patched the stale attribute on the dns package. When the hook subsequently executed import dns.asyncresolver, it found no entry in sys.modules, loaded a fresh real module, and bypassed the mock entirely.

Python 3.12 uses pkgutil.resolve_name, which performs a real import and self-heals, explaining why the test failure is not identified in my local test.

Added a stable_dns_import fixture for both SRV test classes.

This fixture re-registers the submodules:

importlib.import_module("dns.resolver")
importlib.import_module("dns.asyncresolver")

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Drafted-by: Claude Code (Sonnet 5); reviewed by @gtxu

[ashb]

Small nit