build(crate): Add a new zebra-grpc crate

[oxarbitrage]

Motivation

We want to create a new crate zebra-grpc and develop scanner related rpc queries there. Close #8161

PR Author Checklist

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Solution

This just add the basics used to create the crate placeholder. I think we might want to add more stuff as we need it but feel free to request now.

This PR makes the zebra-grpc crate depend on zebra-scan and tonic.

Review

Anyone can review.

Reviewer Checklist

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• Does the PR scope match the ticket?
• Are there enough tests to make sure it works? Do the tests cover the PR motivation?
• Are all the PR blockers dealt with?
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Follow Up Work

This will unlock #8162 and #8164 and further work in the zebra-grpc crate.