Add support for creating and maintaining OIDC Metadata

MOIDC support will be part of the distributed IdP with v4.1

Note:  You need to use the "profile of SAML metadata for OIDC", not the JSON format, if you want to take advantage of metadata-driven relying party overrides, embedded entity attributes to drive attribute release etc.

Additional Information:

• OIDC metadata:  OPMetadataClientRegistration
• Many of the same overrides, and a similar approach to controlling attributes released, can apply to OIDC integrations.
• University of Illinois is very interested in this functionality being included in SHIBUI.  They currently use OIDC metadata and have go generate the metadata by hand.

Metadata Examples:

https://shibboleth.atlassian.net/wiki/spaces/SC/pages/1912406916/OAuthRPMetadataProfile