Add DataSync example snippets and feature-support entry

[techwritermat]

Summary

• Adds examples/snippets/api/datasync_example_test.go with the 52 doc-pipeline snippets referenced by the new Go DataSync documentation (create/get/get-all/set/update/remove for users, channels, memberships, entities, and relationships, plus the event listener, projection-channel subscription, and two grant-token examples).
• Adds setPubnubExampleDataSyncConfigData to config_helper.go, mirroring the existing PAM helper, reading DS_PUBLISH_KEY/DS_SUBSCRIBE_KEY/DS_SECRET_KEY (already present as CI secrets in .github/workflows/run-tests.yml).
• Registers the data-sync feature group in .pubnub.yml with the 34 DataSync feature keys already defined in the docs repo's registry, so the docs feature-support matrix build doesn't crash for this SDK.

Every example function seeds and cleans up its own running-example data (hidden from the rendered doc snippet via snippet.hide/snippet.show) so it's safe to run individually, repeatedly, or out of order. Every function ends with a deterministic // Output: comment (status codes only, never a dynamically generated id, timestamp, or eTag), which is required for go test to register an Example as a runnable test at all.

Known external dependency

The entity and relationship examples assume the product and ProductOwner classes already exist on the DS_* test keyset via the Admin API — the Go SDK has no method to create classes itself. If those classes aren't provisioned there yet, only those specific examples will fail in CI, independent of this change.

Test plan

• go build ./... clean
• go vet ./examples/... clean (only 2 pre-existing unrelated warnings in getting_started.go/onboarding.go)
• gofmt -l clean on the new/changed files
• All 52 functions confirmed discoverable via go test ./examples/snippets/api/... -list '.*' (0 before this fix — a first pass omitted // Output: comments, which silently excludes an Example from go test's test list entirely)
• Real execution against the DS_* keyset (requires CI, not available locally)

🤖 Generated with Claude Code

[pubnub-ops-terraform]

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