gRPC spec update: make metadata APIs more like the data API

[zehiko]

What

As part of simplifying metadata APIs and as pre-req for creating gRPC catalog data source, we:

• expose only single API for querying metadata (that supports filtering and projection)
• this API now returns a stream of chunks, same as the data API

Testing done

• integrated changes into SN

[github-actions]

Web viewer built successfully. If applicable, you should also test it:

• I have tested the web viewer

Result	Commit	Link
✅	077f041	https://rerun.io/viewer/pr/8292

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[github-actions]

Latest documentation preview deployed successfully.

Result	Commit	Link
✅	5248fdd	https://landing-7yuuqmu9y-rerun.vercel.app/docs

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