Provide devcontainer for local development tooling

Background

This project requires installing at least, not including the codebase dependencies, on various developer laptops:

• gecko
• go (w/ shfmt)
• node (w/ prettier)
• python (w/ poetry)

A devcontainer aims to help situations that arise from the above, including:

• tool installation overhead, tooling is installed at container build
• prevent version mismatches, versions are declared/pinned versions in the Dockerfile, bumped as needed
• separate developer's native laptop environment from project's, preventing conflicts with other projects
• containerized environment, less harm to potentially sensitive workspaces

Also important, use of the devcontainer:

• requires a container runtime (colima, docker desktop, rancher desktop)
• is optional

Acceptance Criteria

• the devcontainer installs the required tooling to develop, lint, test
• at least one other person can use the devcontainer

Definition of Done

• Solution is captured as code and/or documentation and merge requests have been submitted
• Code review completed and merge request approved/merged