Outdated documentation on implementing metadata plugins

[maxnoe]

Description

The documentation mentions a DIDMetadataPlugin, but the link in that class just links to the homepage of the documentation and this class doesn't seem to be defined in the current repository.

https://rucio.github.io/documentation/operator/did_meta/#how-to-develop-a-custom-metadata-solution

Steps to reproduce

Go to the above documentation link

Rucio Version

Current release

Additional Information

No response

[rdimaio]

The DidMetaPlugin exists: https://github.com/rucio/rucio/blob/master/lib/rucio/core/did_meta_plugins/did_meta_plugin_interface.py, but the documentation had a wrong link that linked to the homepage instead of the plugin code. @voetberg opened a PR to fix this: rucio/documentation#302

For future issues relating to the documentation, please open them in the documentation repository: https://github.com/rucio/documentation

[maxnoe]

@rdimaio thanks! For some reason I searched for DIDMetadataPlugin not DIDMetaPlugin