chore(docs/admin/infrastructure): call out and link to awsiamrds auth for aws rds (#15955)

Call out AWS IAM RDS db auth and clarify URL encoding requirement in postgres URL

docs/admin/infrastructure/architecture.md

@@ -94,7 +94,8 @@ external PostgreSQL 13+ database for production deployments.
 
 A managed PostgreSQL database, with daily backups, is recommended:
 
-- For AWS: Amazon RDS for PostgreSQL
+- For AWS: Amazon RDS for PostgreSQL (preferably using
+  [RDS IAM authentication](../../reference/cli/server.md#--postgres-auth)).
 - For Azure: Azure Database for PostgreSQL
 - Flexible Server For GCP: Cloud SQL for PostgreSQL
 

docs/reference/cli/server.md

@@ -948,7 +948,7 @@ The directory to cache temporary files. If unspecified and $CACHE_DIRECTORY is s
 | Type        | <code>string</code>                   |
 | Environment | <code>$CODER_PG_CONNECTION_URL</code> |
 
-URL of a PostgreSQL database. If empty, PostgreSQL binaries will be downloaded from Maven (https://repo1.maven.org/maven2) and store all data in the config root. Access the built-in database with "coder server postgres-builtin-url".
+URL of a PostgreSQL database. If empty, PostgreSQL binaries will be downloaded from Maven (https://repo1.maven.org/maven2) and store all data in the config root. Access the built-in database with "coder server postgres-builtin-url". Note that any special characters in the URL must be URL-encoded.
 
 ### --postgres-auth
 
@@ -959,7 +959,7 @@ URL of a PostgreSQL database. If empty, PostgreSQL binaries will be downloaded f
 | YAML        | <code>pgAuth</code>              |
 | Default     | <code>password</code>            |
 
-Type of auth to use when connecting to postgres.
+Type of auth to use when connecting to postgres. For AWS RDS, using IAM authentication (awsiamrds) is recommended.
 
 ### --secure-auth-cookie