feat(gcp): API Gateway apis + configs + gateways

[NitinKumar004]

Summary

Adds the Google API Gateway control plane (apigateway.googleapis.com) as a new GCP wire service: apis, their apiConfigs, and gateways, plus the long-running operations their mutating RPCs return. Control-plane only (no data plane / request routing).

Provider tier — google-beta, /v1beta/

API Gateway's Terraform resources (google_api_gateway_api, google_api_gateway_api_config, google_api_gateway_gateway) exist only in the google-beta provider, whose default base path is apigateway.googleapis.com/v1beta/ (confirmed against the live v1beta discovery doc — note it is v1beta, not v1beta1). The handler is version-aware and serves both /v1beta/ and /v1/ (a real google.golang.org/api/apigateway/v1 client / gcloud). The completed-operation response carries a version-matched @type (…apigateway.v1beta.* vs …apigateway.v1.*).

Because the shared GCP LRO poller only owns the /v1/ operations space, and the google-beta provider polls operations at its /v1beta/ base path, the handler serves its own /v1beta/ operation polls and yields the /v1/ ones to the shared poller (still registering created ops there so a /v1/ SDK poll resolves the typed response).

Behavior

• LRO resolve-immediately: every mutation returns Operation{done:true} with the resource embedded as a typed Any, so a Terraform/SDK wait terminates on the first poll.
• Computed-field stability (drift points): name, createTime, state (seeded ACTIVE), plus serviceConfigId (config) and defaultHostname (gateway) minted once at create, stored, and stable across reads. openapi_documents contents round-trip byte-for-byte via raw passthrough.
• Hierarchy + cascade: configs nest under apis/{api}/configs; creating a config validates its parent api (404); creating a gateway validates its apiConfig reference (404). Deleting an api cascades to its configs with a trailing-slash-bounded prefix scan (deleting a1 never touches a10).
• updateMask top-level replace; unmasked fields survive. Client-named create via ?apiId=/?apiConfigId=/?gatewayId= (body-name fallback). COW memstore, deep clone on read, Snapshottable.

Note on layout

services/apigateway/driver is already the AWS Amazon API Gateway (REST-API-v1) service — a wholly different API. To avoid corrupting coveragegen (one service dir = one primary interface), the GCP portable driver lives in services/apigatewaygcp/driver. The provider/server package dirs stay apigateway (distinct import trees under gcp/ vs aws/), and the generated GCP page is still docs/coverage/gcp/apigateway.md (page name derives from the provider field, not the service dir). The AWS driver is untouched.

Terraform plan-clean e2e (real google-beta provider, /v1beta/)

Served on :18063, api_gateway_custom_endpoint = http://127.0.0.1:18063/v1beta/, provider hashicorp/google-beta v8.1.0:

• apply — an api + an api_config (openapi document, labels) + a gateway referencing the config → 3 added, LRO did not hang, all states ACTIVE.
• plan -detailed-exitcode → exit 0, no drift (name / service_config_id / default_hostname / openapi contents all stable).
• update display_name + labels on all three → applied (api via PATCH); plan → exit 0; computed fields unchanged.
• destroy → 3 destroyed; api/config/gateway all 404 (cascade verified).

Outputs on apply: api_name = projects/cloudemu-local/locations/global/apis/my-api, service_config_id = my-config-ba0fb7c7, default_hostname = my-gw-dfb2df49.us-central1.gateway.dev.

Gates (GOMAXPROCS=3)

go build ./..., full go vet ./..., gofmt, golangci-lint on new+wired pkgs (0 issues), go test -race new pkgs, full go test ./server/gcp/... (no sibling operations-404 regression), go test ./providers/..., go test ./persist/... (completeness), go test ., and go generate idempotency — all green. Docs regenerated: only the new gcp/apigateway.md + shared indexes; AWS apigateway.md untouched.