add dockerfiles for development on cpu and gpu

[liam-adams]

Motivation and Context

This is for issue https://github.com/quantumblacklabs/causalnex/issues/19

How has this been tested?

I ran make test, make package and installed causalnex from source inside both of the docker containers. All tests passed and I ran the tutorial https://causalnex.readthedocs.io/en/latest/03_tutorial/01_first_tutorial.html on the created pip package

In the gpu image I ran into the same issue described here https://github.com/quantumblacklabs/causalnex/issues/138

Checklist

• [y] Read the contributing guidelines
• [n/a] Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• [y] Updated the documentation to reflect the code changes
• [n] Added a description of this change and added my name to the list of supporting contributions in the RELEASE.md file
• [n/a] Added tests to cover my changes
• [y] Assigned myself to the PR

Notice

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