Add Welcome Bot to create an inclusive environment for new contributors

[Tlazypanda]

Is your feature request related to a problem? Please describe.
Welcome is a simple way to welcome new users based off maintainer defined comments.

The 3 plugins it combines with are new-issue-welcome(Comment to be posted to on first time issues) , new-pr-welcome(Comment to be posted to on PRs from first time contributors in your repository) and first-pr-merge(Comment to be posted to on pull requests merged by a first time user).

Describe the solution you'd like
We can setup Welcome bot by adding the GitHub App to our organization repositories and configuring .github/config.yml according to the content of the messages we want.

This will make the new contributors feel welcomed and at ease in interacting with the community.

Additional context
Screenshots that depict the Welcome bot in action:

[Tlazypanda]

Hey @leitchy Just adding this issue since this bot needs to be setup in other repositories as per discussion with @gmajan 😅 Thanks ✌️