docs(glue): add usage of SECRET_ID (#21905)

This PR is to resolve #21190.
I add an example of `Connection` with RDS secret to the documentation.
This PR will help RDS customers understand how to create more secure `Connections`.

----

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### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: WinterYukky

packages/@aws-cdk/aws-glue/README.md

@@ -108,6 +108,24 @@ new glue.Connection(this, 'MyConnection', {
 });
 ```
 
+For RDS `Connection` by JDBC, it is recommended to manage credentials using AWS Secrets Manager. To use Secret, specify `SECRET_ID` in `properties` like the following code. Note that in this case, the subnet must have a route to the AWS Secrets Manager VPC endpoint or to the AWS Secrets Manager endpoint through a NAT gateway.
+
+```ts
+declare const securityGroup: ec2.SecurityGroup;
+declare const subnet: ec2.Subnet;
+declare const db: rds.DatabaseCluster;
+new glue.Connection(this, "RdsConnection", {
+  type: glue.ConnectionType.JDBC,
+  securityGroups: [securityGroup],
+  subnet,
+  properties: {
+    JDBC_CONNECTION_URL: `jdbc:mysql://${db.clusterEndpoint.socketAddress}/databasename`,
+    JDBC_ENFORCE_SSL: "false",
+    SECRET_ID: db.secret!.secretName,
+  },
+});
+```
+
 If you need to use a connection type that doesn't exist as a static member on `ConnectionType`, you can instantiate a `ConnectionType` object, e.g: `new glue.ConnectionType('NEW_TYPE')`.
 
 See [Adding a Connection to Your Data Store](https://docs.aws.amazon.com/glue/latest/dg/populate-add-connection.html) and [Connection Structure](https://docs.aws.amazon.com/glue/latest/dg/aws-glue-api-catalog-connections.html#aws-glue-api-catalog-connections-Connection) documentation for more information on the supported data stores and their configurations.

packages/@aws-cdk/aws-glue/rosetta/default.ts-fixture

@@ -6,6 +6,7 @@ import * as glue from '@aws-cdk/aws-glue';
 import * as s3 from '@aws-cdk/aws-s3';
 import * as ec2 from '@aws-cdk/aws-ec2';
 import * as kms from '@aws-cdk/aws-kms';
+import * as rds from '@aws-cdk/aws-rds';
 
 class Fixture extends Stack {
   constructor(scope: Construct, id: string) {