* Add resource for (Glance) Metadata Definition Schema API
(https://docs.openstack.org/api-ref/image/v2/metadefs-index.html?expanded=#metadata-definition-schemas)
* Adjust names to avoid abbreviations
* Adjust grouping
* Add tests
* Add docs and release note
* Trim underlines in docs
* Resolve merge conflict
* Seperate functional test to another file
* Rename test class name correctly
Change-Id: If2dfbca5ffbd425e4183b310af9534411318a395