chore: added cascade delete section for Has Many and Has One relation…

[tejas2008]

Description of changes:

Enhanced Documentation for Data Modeling Relationships

1. "Has One" Relationship Updates

• Added a new subsection detailing cascade delete functionality
• Incorporated code snippets using existing examples to illustrate the process

2. "Has Many" Relationship Updates

• Introduced a dedicated segment explaining cascade delete operations
• Provided practical code examples based on current documentation to demonstrate implementation

Related GitHub issue #, if available:

• #273
• Amplify Flutter SIM

Instructions and Testing

• Tested changes locally using fork of aws-amplify docs repo.
• Verified the code snippets by creating a Gen-2 amplify project and replicated schemas and cascade delete functionality.
• Below are the images from locally generated docs:
  • Has One
  • Has Many

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.