(chore): Export UserProvider type and add it to toc.yaml (#1165)

- Export UserProvider type
- Add UserProvider to toc.yaml

Author: lahirumaramba

docgen/content-sources/node/toc.yaml

@@ -94,6 +94,8 @@ toc:
     path: /docs/reference/admin/node/admin.auth.UserProviderRequest
   - title: "UserRecord"
     path: /docs/reference/admin/node/admin.auth.UserRecord
+  - title: "UserProvider"
+    path: /docs/reference/admin/node/admin.auth.UserProvider
   - title: "SessionCookieOptions"
     path: /docs/reference/admin/node/admin.auth.SessionCookieOptions
   - title: "BaseAuth"

etc/firebase-admin.api.md

@@ -403,7 +403,6 @@ export namespace auth {
         tokensValidAfterTime?: string;
         uid: string;
     }
-    {};
 }
 
 // @public (undocumented)

src/auth/index.ts

@@ -156,7 +156,7 @@ export namespace auth {
   /**
    * Represents a user identity provider that can be associated with a Firebase user.
    */
-  interface UserProvider {
+  export interface UserProvider {
 
     /**
      * The user identifier for the linked provider.