Adopt AIP 151 operations

[STRRL]

Problem

Import and discovery jobs run in the background, but their Create APIs return custom responses. Clients cannot use the standard long running operation contract.

Solution

Return google.longrunning.Operation from both Create APIs and expose the standard Operations service. Keep ImportRun and DiscoveryRun as stored resources for progress and history.

Major Changes

• API contract
  • Add AIP 151 operation metadata and response types
  • Generate standard Google Operations clients
• Operation service
  • Support GetOperation and WaitOperation
  • Return typed metadata, successful responses, and structured errors
  • Return ABORTED when another run is active
• Web client
  • Register operation Any message types
  • Add the generated Operations client

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Note

Medium Risk
This is a breaking RPC contract change for CreateImportRun/CreateDiscoveryRun; callers must use Operations polling and Any unpacking, though the in-repo frontend is updated in the same PR.

Overview
CreateImportRun and CreateDiscoveryRun now return google.longrunning.Operation instead of bespoke create responses. Progress lives in operation metadata (ImportRunMetadata / DiscoveryRunMetadata with the run resource); success and failure use Operation.response and Operation.error. GetImportRun, ListImportRuns, GetDiscoveryRun, and ListDiscoveryRuns stay for history.

Buf pulls in googleapis, adds a second generate pass for google.longrunning.Operations (Go Connect + TS), and marks generated trees as linguist-generated. The web app registers metadata/response types on the Connect JSON registry, exports an operationsClient, and startDiscovery reads the run name from unpacked operation metadata instead of a direct run field.

Docs/ADR now describe AIP 151 polling via GetOperation, one active import or discovery per workspace with parallel creates returning ABORTED, and the standard operation shape.

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