doc: add external postgres database for olake-ui

docs/install/olake-ui/index.mdx

@@ -132,6 +132,73 @@ x-app-defaults:
 
 This will create and use `/custom/path/to/olake-data` instead of the default `./olake-data` directory.
 
+### External PostgreSQL Configuration
+
+OLake supports using an **external PostgreSQL instance** instead of the built-in Postgres service included in the docker-compose file. PostgreSQL stores all job data, configurations, sync state, and Temporal workflow data.
+
+**Configure `docker-compose.yml`**
+
+The compose file can be downloaded from the OLake UI repository:
+```bash
+curl -o docker-compose.yml https://raw.githubusercontent.com/datazip-inc/olake-ui/refs/heads/master/docker-compose.yml
+```
+
+Within the compose file, an extension field named `x-db-envs` defines all database configuration values used by OLake and Temporal:
+
+```yaml
+x-db-envs:
+  DB_HOST: &DBHost postgresql
+  DB_PORT: &DBPort 5432
+  DB_USER: &DBUser temporal
+  DB_PASSWORD: &DBPassword temporal
+  DB_SSLMODE: &DBSSLMode disable
+  OLAKE_DB_NAME: &olakeDBName postgres
+  TEMPORAL_DB_NAME: &temporalDBName temporal
+```
+
+These values use YAML anchors `(&name)`, enabling reuse across multiple services.
+To connect to an external PostgreSQL instance, the values in this section can be updated accordingly. All dependent services (olake-ui, temporal-worker, and temporal) will automatically read and use the updated configuration.
+
+**TLS settings for external Temporal database**
+
+The compose file includes optional TLS-related variables for Temporal's SQL connection:
+
+```yaml
+  # SQL_TLS: true
+  # SQL_TLS_DISABLE_HOST_VERIFICATION: true
+  # SQL_TLS_ENABLED: true
+  # SQL_HOST_VERIFICATION: false
+```
+
+These values remain commented by default because the built-in PostgreSQL container does not require TLS.
+When Temporal is configured to use an external PostgreSQL instance particularly one with SSL/TLS enabled, these variables can be uncommented and configured as needed.
+
+**Separate database for Temporal**
+
+Temporal can also be configured to use a dedicated PostgreSQL database, separate from the database used for storing OLake metadata and job-related information. This configuration is achieved by overriding the Temporal-specific environment variables in the service definition:
+
+```yaml
+temporal:
+  environment:
+    DB: postgres12
+    POSTGRES_SEEDS: <DATABASE_HOST_NAME>
+    DB_PORT: <DATABASE_PORT>
+    POSTGRES_USER: <DATABASE_USER>
+    POSTGRES_PWD: <DATABASE_PASSWORD>
+    DBNAME: <TEMPORAL_DATABASE_NAME>
+    ENABLE_ES: true
+    ES_SEEDS: elasticsearch
+    ES_VERSION: v7
+    TEMPORAL_ADDRESS: temporal:7233 # temporal service address
+    TEMPORAL_CLI_ADDRESS: temporal:7233 # temporal cli address
+
+    # for external postgres database
+    SQL_TLS: true
+    SQL_TLS_DISABLE_HOST_VERIFICATION: true
+    SQL_TLS_ENABLED: true
+    SQL_HOST_VERIFICATION: false
+```
+
 ### Service Environment Variables
 
 Key environment variables that can be customized within specific services: