Refactor password reset to use dedicated Keycloak admin client

- Add Keycloak admin credentials configuration to environment variables
- Extract Keycloak admin operations into reusable utility module
- Refactor forgot-password endpoint to use new admin client utility
- Add documentation for Keycloak custom login implementation
- Add password reset fix summary documentation

This improves code organization by separating admin operations from
business logic and provides proper admin credentials for Keycloak
API operations instead of using regular client credentials.

utils/types.ts

@@ -87,6 +87,12 @@ export interface KeycloakConfig {
   callbackUrl: string;
 }
 
+export interface KeycloakAdminConfig {
+  issuer: string;
+  clientId: string;
+  clientSecret: string;
+}
+
 export interface NocoDBConfig {
   url: string;
   token: string;