[Go] Add retriever plugin for firestore vector store
Looks like it was added in the Firestore Go SDK https://github.com/googleapis/google-cloud-go/releases/tag/firestore%2Fv1.16.0
Not 100% sure whether firestore vector store retriever should be part of firebase plugin (doesn't currently exist)... or google cloud plugin... or a standalone plugin. Perhaps worth a discussion on discord.
https://github.com/firebase/genkit/pull/1079
rebased that PR on main and added docs, sample.
https://github.com/firebase/genkit/pull/1079 PR into main
rebased:
https://github.com/firebase/genkit/pull/1165
onto next
rebased against main https://github.com/firebase/genkit/pull/1470