Fixes #2664: Added workflow to automate PR to develop branch on merge to master branch

[PawanPatil19]

This PR fixes #2664.

As mentioned in the issue, I created a Github Action workflow to create a pull request from 'master' branch to 'develop' branch on any merge in the 'master' branch.

Technical details

• I used actions/checkout@v2 to check out the repository's code, followed by repo-sync/pull-request@v2 which creates the pull request.
• The title of the pull request stays the same as the commit message/merge message if any specific instructions is not given in the workflow.
• I have also added a auto-pr label to the incoming pull requests, which could be changed in the workflow.

Note
For this action to work you must explicitly allow GitHub Actions to create pull requests. This setting can be found in a repository's settings under Actions > General > Workflow permissions.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the develop branch of the repository
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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