Added pre-commit type-checking

[miriamcheng]

Description

Added pre-commit type-checking using mypy.
Written by Mekaeel and Miriam

Pre-commit type-checks and style-checks (not yet) your code before you commit them. It is recommended that you do this before making commitments.
STEP 1: Install pre-commit
pip install pre-commit
STEP 2: Set up pre-commit hooks: navigate to local repository and activate pre-commit hooks

cd /path/to/your/project
pre-commit install

STEP 3: Test pre-commit hooks
pre-commit run --all-files
By doing this, users can help to identify and fix issues before they are committed to the repository.

Issues Resolved

This contributes to issue #92, but we still need to verify that all types are working. It clearly shows issues for cluster-bootstrapping.py which need to be addressed.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[dtaivpp]

Okay, two small changes and then I think we should be good.

1. Can we move this into the .pre-commit-config.yaml that lives at demo/.pre-commit-config.yaml?

2. Lets convert this from a remote hook (using the GitHub repo link) to a local hook (see this documentation). That will probably help solve some issues we may have with modules not getting found.