fix: [#1] update default API token from local-dev-admin-token-12345 to MyAccessToken in local environment

- Ensures consistency with documentation and configuration templates
- Resolves API authentication failures in E2E tests
- All environment configs now use the standardized MyAccessToken

Author: josecelano

infrastructure/config/environments/local.env

@@ -14,7 +14,7 @@ MYSQL_USER=torrust
 MYSQL_PASSWORD=tracker_secret_local
 
 # Tracker API Token
-TRACKER_ADMIN_TOKEN=local-dev-admin-token-12345
+TRACKER_ADMIN_TOKEN=MyAccessToken
 
 # Grafana Admin Credentials
 GF_SECURITY_ADMIN_USER=admin