Create greeting bot using Github Actions for new pull requests and issues

## Background
We'd like to add a greeting bot that provides a comment when a new pull request or issue is made

# Solution
Use Github Actions to create a greeting bot for new issues and new pull requests in the Open-Sentencing-Aggregator
repository.

Learn more about Github Actions [here](https://docs.github.com/en/actions/learn-github-actions/understanding-github-actions#create-an-example-workflow):

## Tasks
- Use [this greeting bot an example ](
https://github.com/Call-for-Code-for-Racial-Justice/Five-Fifths-Voter/blob/main/.github/workflows/greetings.yml)
- Read about Github Actions
- Create Github Action, title the yml file`greetings.yml`
- Test Github Action

## Acceptance criteria
- Github action is present in ./github/workflows folder in Open-Sentencing-Aggregator
repo.
- file is named `greetings.yml`
- greetings for PR and issue is as listed in [example](
https://github.com/Call-for-Code-for-Racial-Justice/Five-Fifths-Voter/blob/main/.github/workflows/greetings.yml)