[Enhancement] Add gitpod

[stewartshea]

Observation
Unfortunately gitpod doesn't support the devcontainer format yet: gitpod-io/gitpod#7721
But based on how this devcontainer is created, it should be easy to port to a gitpod.yml file for those who use that service. I've tried both, but since we don't need to run any other container images locally (with the remote services being served up in the RunWhen sandbox), I'd prefer to stick to gitpod (since I pay for it and found that I ran out of cpu hours on codespaces last month).

Current Outcome

• No gitpod.yml exists

Desired Outcome

• gitpod.yml that mimics the devcontainer setup