ENH: Allow insert/update/delete and files in Extern C

Summary

See https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/412

Focus

Point the reviewer to the core of the code change. Where should they start
reading? What should they focus on (e.g. security, performance,
maintainability, user-friendliness, compliance with the specs, finding more
corner cases, concrete questions)?

Test Environment

How to set up a test environment for manual testing?

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Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

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.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.

doc/Examples.rst

@@ -224,11 +224,11 @@ Up- and Download a file
   const auto &insert_results = insert_transaction->GetResultSet();
   const auto &inserted_file = insert_results.at(0);
 
-  // for the download you need to use the RetrieveAndDownloadFilesById task and
+  // for the download you need to use the RetrieveAndDownloadFileById task and
   // supply the path where the file shall be stored
   test_download_file = fs::path("test_download_file_delete_me.dat");
   auto download_transaction(connection->CreateTransaction());
-  download_transaction->RetrieveAndDownloadFilesById(
+  download_transaction->RetrieveAndDownloadFileById(
       inserted_file.GetId(), test_download_file.string());
   download_transaction->ExecuteAsynchronously();
   download_transaction->WaitForIt().GetCode()