Merge branch 'f-doc-xml' into 'dev'

.gitignore

.gitlab/merge_request_templates/Default.md

CHANGELOG.md

src/doc/Makefile

src/doc/development/api/xml/Makefile

src/doc/development/api/xml/caosdb_openapi.yaml

src/doc/development/api/xml/openapi_config.json

src/doc/index.rst

src/doc/specification/Entity_Overview.md

src/doc/specification/entity_api.rst

src/doc/specification/index.rst