chore(Swift): Updating supported Xcode versions

[harsh62]

Description of changes:

The aim of the PR is to fix the minimum supported version of Xcode in Amplify Swift.

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.

[ruisebas]

Since now all platforms have the same Xcode requirement, would it be simpler to call it out once?

Something like:

## Prerequisites
- Xcode 15.0 or later.
- An application with Amplify libraries integrated an a minimum target of any of the following:
  - iOS 13.0
  - macOS 10.15
  - // etc