fix(controlplane): correct OpenAPI types for json.RawMessage and []byte fields

[mekilis]

Summary

• json.RawMessage fields (datastore.Event.data, datastore.Metadata.data, ProjectEventType.json_schema) leaked Go's []byte representation into the OpenAPI spec as array of integer; generated SDK clients then typed event payloads as list[int] instead of arbitrary JSON. Annotated them swaggertype:"object", matching the existing convention on api/models/event.go request models.
• GooglePubSubConfig.ServiceAccount []byte is now documented as a base64 string (format: byte), which is what encoding/json actually puts on the wire.
• CreateDynamicEvent's @Success 201 now documents util.ServerResponse{data=Stub}, matching the handler's actual util.NewServerResponse(...) envelope and its sibling create-event endpoints.
• Regenerated docs/ via make generate_docs; no integer-array-typed fields remain in the spec.

Caught by SDK generation review on the first generated Python client PR (frain-dev/convoy-python#21): event data came out as list[int].

Test plan

• make generate_docs clean; openapi spec validate passes
• Spec audit: zero remaining array-of-integer properties; data/json_schema are object, service_account is base64 string
• go build / go vet / golangci-lint clean on touched packages (annotation-only change, no runtime behavior)

[cursor]

Current version of PR was reviewed by /review-bugbot on Jul 19, 20:50 GMT+1. It flagged 0 findings.

^{Bugbot on commit dd483a7 is skipped.}