Add --against-registry flag for buf breaking

[sergunya]

This PR adds a --against-registry flag to buf breaking that can be
set in lieu of --against. When --against-registry is set, breaking checks
are run against the latest commit on the default label of the remote module
in the registry.

buf breaking will error if one of --against or --against-registry is
not set:

$ buf breaking
Failure: Must set --against or --against-registry

buf breaking --against-registry will error if not all modules in the input
are named (and thus a remote cannot be resolved):

$ buf breaking --against-registry
Failure: cannot use --against-registry with unnamed module, proto/local

Fixes bufbuild#3654

[sergunya]

@dpaia-validator validate

[dpaia-validator]

✅ Datapoint verification passed.

Instance: bufbuild__buf-3696
Duration: 93s
Criteria: compilation: pass, baseline_tests: pass, patch_applied: pass, tests: pass, fail_to_pass: pass, pass_to_pass: pass, fail_to_fail: skipped
Tests: Total: 183, Passed: 183, Failed: 0, Skipped: 0
FAIL_TO_PASS: pass: all fail_to_pass tests fixed

Details: Workflow run