[manjari25]

Why?

The tango analyzer and its client adapter have no way to run in the reference orchestrator. This wires them in so a queue can select analyzer: tango.

What?

• tangoclient: Dial opens a lazy gRPC connection to Tango. Connection.ChangedTargetsClient builds the adapter for a remote and a strategy (unset, shell or native, required).
• Config: a top-level tango block (address, signatureCacheBytes) and a per-queue analyzer.tango block (remote, strategy). Neither strategy nor the top-level settings have defaults.
• Validation: the address and a positive cache size are required whenever any queue uses tango, and every tango queue needs a strategy. The builder rejects a tango queue that doesn't use the git change provider.
• Builder: one shared signature cache, a per-queue MySQL signature store, and the base revision read from the queue's own clone. Base-revision fetches take the same gitrepo.Repo lock as the git change provider.
• README: the new config keys and two limits. Tango needs a git-provider queue until the GitHub base revision exists, and native needs github:// URIs that the git provider doesn't emit.

Test Plan

• bazel test //service/submitqueue/orchestrator/server/... //submitqueue/extension/conflict/tango/... covers the config validation, the builder and the adapter.
• CI.

Issue