Add missing code highlight to OpenSearch page

[Yono1112]

Description of changes:

Added missing code highlighting to the code block in the Connect to Amazon OpenSearch for search and aggregate queries under Step 2: Setting Up the OpenSearch Instance.

The updated code block is as follows:

// Create the OpenSearch domain
const openSearchDomain = new opensearch.Domain(
  backend.data.stack,
  'OpenSearchDomain',
  {
    version: opensearch.EngineVersion.OPENSEARCH_2_11,
    nodeToNodeEncryption: true,
    // set removalPolicy to DESTROY to make sure the open search domain is deleted on stack deletion.
    removalPolicy: RemovalPolicy.DESTROY,
    encryptionAtRest: {
      enabled: true
    }
  }
);

Adding this highlight improves readability, making it easier for users to identify and understand the code structure for configuring OpenSearch.

Related GitHub issue #, if available:

Instructions

If this PR should not be merged upon approval for any reason, please submit as a DRAFT

Which product(s) are affected by this PR (if applicable)?

• amplify-cli
• amplify-ui
• amplify-studio
• amplify-hosting
• amplify-libraries

Which platform(s) are affected by this PR (if applicable)?

• JS
• Swift
• Android
• Flutter
• React Native

Please add the product(s)/platform(s) affected to the PR title

Checks

• Does this PR conform to the styleguide?

• Does this PR include filetypes other than markdown or images? Please add or update unit tests accordingly.

• Are any files being deleted with this PR? If so, have the needed redirects been created?

• Are all links in MDX files using the MDX link syntax rather than HTML link syntax?
  
  ref: MDX: [link](https://docs.amplify.aws/)
  HTML: <a href="https://docs.amplify.aws/">link</a>

When this PR is ready to merge, please check the box below

• Ready to merge

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[josefaidt]

Hey @Yono1112 thanks for taking the time to file this! Change looks good 🙂