F multi retrieve

Summary

Implements multi-entity retrieval caosdb/customers/lfpb/management#393

See tests in caosdb-cppinttest!4 (merged)

Focus

• Most relevant changes are in include/caosdb/transaction.h and src/caosdb/transaction.cpp.
• New class MultiResultSet represents a result set with multiple entities. Is this a good name?
• New enum TransactionType restricts the kind of sub-transactions (Insert, Delete, Retrieve) which can be added to a transaction.
• Macros are used to check whether InsertEntity, DeleteById or RetrieveById can be called on a transaction (given the TransactionStatus and 'TransactionType`).

Test Environment

Test with server in branch f-grpc-f-multi-retrieve

Check List for the Author

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• All automated tests pass
• Reference related Issues
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  • Intent of new code
  • Problems with old code
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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
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
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src/caosdb/configuration.cpp

@@ -38,6 +38,7 @@
 #include <cassert>                                     // for assert
 #include <cstdlib>                                     // for getenv
 #include <exception>                                   // IWYU pragma: keep
+#include <cstring>                                     // for strcmp
 #include <grpcpp/security/credentials.h>               // for SslCredentials
 #include <iterator>                                    // for next
 #include <map>                                         // for map