DOC: Document the XML API

Summary

See https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/238 and https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/407. Introduce a minimal documentation of the specifications of the XML API using openAPI.

Focus

The formulation of the API is in src/doc/development/api/xml/caosdb_openapi.yaml. Some text and a new section for the entity API have been added to the Specifications section, but since openapi-codegen fails to produce reasonable output, we leave it to gitlab to render the specification and just link to the file blob.

Test Environment

make doc and have a look at the section in Specification.

Check List for the Author

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 spezifications? Are they satisfied?

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

src/doc/specification/Entity_Overview.md

-# Specification of the Entity API
+# Overview of the CaosDB Entities' structure
 
-**Warning:** This specification is outdated. It is included to serve as a starting point for a more up-to-date description of the entity API.
+**Warning:** This overview may be outdated.
 
 Version: 0.1.0r1