Update Contributing.md Guide

[dawoodkhan82]

Provide more details and steps for setting up local dev environment and start running/debugging a demo.

[abidlabs]

It seems a lot of people also get stuck when using Codespaces so it'd be nice to make sure that DX flow is streamlined. Related issue: #2343

[abidlabs]

A few other things I noticed @dawoodkhan82:

• we no longer use CircleCI so this should be removed from contributing.md
• we have added a linter but this is not mentioned in contributing.md

Also the PR template is a little bloated, perhaps we can trim that a bit as well

[thepelkus-too]

A note on testing in that document:

Under Continuous Integration and Testing it says:

All PRs must pass the continuous integration tests before merging. To test locally, you can run python -m unittest from the repo directory.

When I ran that command, no tests were run. However, when I ran the test command from the Extra tidbits:

bash scripts/run_all_tests.sh

it seemed like it might've been doing what I would expect.

I had some difficulties with those tests that might've stemmed from running in the Windows Subsystem for Linux, but I'm not sure just yet; I'll make another note here if I can pin that down.