docs: Enhance PostgreSQL client module documentation

- Add details about the new PostgreSQL installer feature.
- Include prerequisites for installer and basic operations.
- Expand test file descriptions with installer details.
- Add descriptions for installer functions.
- Include example usage for both basic operations and installer.

src/rhai_tests/postgresclient/test_simple.rhai

@@ -0,0 +1,22 @@
+// Simple test script to verify that the Rhai engine is working
+
+print("Hello, world!");
+
+// Try to access the PostgreSQL installer functions
+print("\nTrying to access PostgreSQL installer functions...");
+
+// Try to call the pg_install function
+try {
+    let result = pg_install(
+        "postgres-test",
+        "15",
+        5433,
+        "testuser",
+        "testpassword"
+    );
+    print("pg_install result: " + result);
+} catch(e) {
+    print("Error calling pg_install: " + e);
+}
+
+print("\nTest completed!");