ENH: Support FIND and COUNT queries

Summary

See https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/399. Introduces FIND and Count queries.

Focus

Most changes are in transaction.h and transaction.cpp.

Test Environment

Unit and integration tests with server in f-grpc-f-query

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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
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src/caosdb/transaction.cpp

@@ -161,8 +161,6 @@ auto Transaction::RetrieveById(const std::string &id) noexcept -> StatusCode {
   return this->status.GetCode();
 }
 
-// TODO(fspreck) What about count queries (mixed with retrievals),
-// what about unique queries?
 auto Transaction::Query(const std::string &query) noexcept -> StatusCode {
   ASSERT_CAN_ADD_QUERY