feat: Support multiple local issuers in oidc-test-support

[tommytroen]

In order to have multiple issuers when using oidc-test-support in dev/local mode you have to configure the same metadata/jwks on all issuers as the FileResourceRetriever only supports one set of files. The TokenGeneratorController also only issues tokens from a single issuer.

When protecting 2 endpoints with different issuers, e.g. @ProtectedWithClaims(issuer="abc") and @ProtectedWithClaims(issuer="xyz"), in local mode you could get a 401 on issuer xyz as only a token for issuer abc has been found and vice versa. This is due to that the issuers are essentially the same.

One solution is to allow to specify file:// in the discoveryurl and let the FileResourceRetriever also support "live" providers over HTTP.