feat(sdk): public client and other enhancements to well-known SDK functionality

[jakedoublev]

Resolves #1373

This PR makes the following changes:

1. provisions a public client to keycloak with an allowlisted redirectUri of http://localhost:9000 to support otdfctl
2. adds a few idP accessor methods to the SDK for reading the well-known configuration of the platform pre-auth
3. removes a few errors about the SDK being unauthenticated now that reading from the well-known pre-auth is a valid SDK use
4. adds a public_client_id to the well-known idP config (with example configs updated) and a warning log about discovery if not provided in the config on startup
5. cannot remove platform_issuer as a top-level well-known config key that is a duplicate of idp.issuer because of this issue sdk should retrieve platform issuer from well-known idp.issuer instead of platform_issuer java-sdk#119

{
  "configuration": {
    "health": {
      "endpoint": "/healthz"
    },
    "idp": {
      "authorization_endpoint": "http://localhost:8888/auth/realms/opentdf/protocol/openid-connect/auth",
      "id_token_signing_alg_values_supported": [
        "PS384",
        "RS384",
        "EdDSA",
        "ES384",
        "HS256",
        "HS512",
        "ES256",
        "RS256",
        "HS384",
        "ES512",
        "PS256",
        "PS512",
        "RS512"
      ],
      "issuer": "http://localhost:8888/auth/realms/opentdf",
      "jwks_uri": "http://localhost:8888/auth/realms/opentdf/protocol/openid-connect/certs",
      "public_client_id": "opentdf-public", // this is new
      "require_request_uri_registration": true,
      "response_types_supported": [
        "code",
        "none",
        "id_token",
        "token",
        "id_token token",
        "code id_token",
        "code token",
        "code id_token token"
      ],
      "subject_types_supported": [
        "public",
        "pairwise"
      ],
      "token_endpoint": "http://localhost:8888/auth/realms/opentdf/protocol/openid-connect/token"
    }
  }
}

[jakedoublev]

Cannot deprecate platform_issuer at top level without doing this first: opentdf/java-sdk#119

[jakedoublev]

Work on this uncovered #1384