APIv1 metadata controller breaks on individual entity metadata

[vladimir-mencl-eresearch]

Imported from upstream #162

I ran into this when exploring the REST API: the APIv1 metadata controller returns as the last entry of the list:

{"name":"entity","description":"SAML 2 compliant metadata snippet for specific entity descriptor ID","format":"xml","type":"entity","functioning":true,"link":"https://registry.tamaki.dev.tuakiri.ac.nz/federationregistry/api/v1/metadata/entity"}

But, when accessing the /federationregistry/api/v1/metadata/entity link, I only get

HTTP Status 400 -
type Status report
message

description The request sent by the client was syntactically incorrect.
Apache Tomcat/7.0.39

When I add the ID of an EntityDescriptor as an parameter, I do correctly get the metadata for that entityDescriptor:

https://registry.tamaki.dev.tuakiri.ac.nz/federationregistry/api/v1/metadata/entity/8

But it looks like the API controller is missing functionality to return a JSON list of entities with links to individual entity metadata URLs, similar to what other controllers do... looks like broken API to me.

Note: this is not used by any client - would be there just for completeness of the API.