WIP: SELECT for GRPC API

Summary

Add messages for the result of SELECT queries based on the sketches which have already been there but unused.

• Server implementation in caosdb-server!72 (merged)
• CPP implementation in caosdb-cpplib!44 (merged)

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• All automated tests pass
• Reference related issues
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Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
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• Check: Are there specifications? Are they satisfied?

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