feat(react-native): Add push notification docs

[cshfang]

Description of changes:

This PR adds public documentation for Amplify Push Notification for React Native

redirects are needed

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
• iOS
• 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://link.com)
  HTML: <a href="https://link.com">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.

[mergify]

@cshfang, since a file was deleted from the src/pages and/or src/fragments directories, redirects might need to be set up so these previous pages do not 404. If redirects are needed, please answer these questions for each redirect that is needed:

• What is the source address of the redirect? (Where are you trying to redirect from?)

• What is the target address of the redirect? (Where are you trying to redirect to?)

• Type of redirect? 301 - permanent redirect or 302 - temporary redirect? (More info on Amplify Hosting redirects here: https://docs.aws.amazon.com/amplify/latest/userguide/redirects.html)

[github-advanced-security]

You have successfully added a new CodeQL configuration /language:javascript. As part of the setup process, we have scanned this repository and found no existing alerts. In the future, you will see all code scanning alerts on the repository Security tab.

[aws-amplify-us-west-2]

This pull request is automatically being deployed by Amplify Hosting (learn more).

Access this pull request here: https://pr-5344.d39agkzf0cwtdz.amplifyapp.com

[cshfang]

@cshfang, since a file was deleted from the src/pages and/or src/fragments directories, redirects might need to be set up so these previous pages do not 404. If redirects are needed, please answer these questions for each redirect that is needed:

• What is the source address of the redirect? (Where are you trying to redirect from?)
• What is the target address of the redirect? (Where are you trying to redirect to?)
• Type of redirect? 301 - permanent redirect or 302 - temporary redirect? (More info on Amplify Hosting redirects here: https://docs.aws.amazon.com/amplify/latest/userguide/redirects.html)

src/pages/lib/push-notifications/overview/q/platform/[platform].mdx
src/pages/lib/push-notifications/working-with-api/q/platform/[platform].mdx ->

src/pages/lib/push-notifications/getting-started/q/platform/[platform].mdx (302)

src/fragments/lib/push-notifications/js/getting-started.mdx
src/fragments/lib/push-notifications/js/overview.mdx
src/fragments/lib/push-notifications/js/working-with-api.mdx ->

src/fragments/lib/push-notifications/common/getting-started.mdx (302)

src/fragments/lib/push-notifications/js/testing.mdx ->

src/fragments/lib/push-notifications/common/testing.mdx (302)

[tannerabread]

Most of my comments are pretty nit-picky but I gotta say I love what you've done with the imports/fragments. We should probably try to make that a standard going forward

[abdallahshaban557]

LGTM

[abdallahshaban557]

LGTM