Add UI for SAML Config

[strazto]

From #2 , but I'd like that to be closed and this opened in-lieu

[9p4]

Will be done as soon as #27 is merged

[strazto]

@9p4 Oh, are you implying you'll implement this?

If so, awesome! I don't really care about SAML personally, so I wasn't that keen to implement it, but as far as I know, the only difference in config fields are:

SAML Only:

samlEndpoint: string. The SAML endpoint.
samlClientId: string. The SAML client ID.
samlCertificate: string. The base64 encoded SAML certificate.

OIDC Only:

oidEndpoint: string. The OpenID endpoint. Must have a .well-known path available.
oidClientId: string. The OpenID client ID.
oidSecret: string. The OpenID secret.

roleClaim
oidScopes 

You may wish to refactor load/saveProvider functions into serializeShared, serializeSAML, serializeOIDC, and it'll probably make sense to group all of the the protocol specific options into the same section.
To reduce duplication, we can probably just hide whichever section doesn't apply to the current provider.