feat(*:skip) Add a .dockerignore file to speed up image builds

[tanertopal]

Issue

Description

This .dockerignorefile ensures that Docker builds don't have to load the .venv into the full context of the build.

Related issues/PRs

Proposal

Explanation

Checklist

• [ ] Implement proposed change
• [ ] Write tests
• [ ] Update documentation
• [ ] Make CI checks pass
• [ ] Ping maintainers on Slack (channel #contributions)

Any other comments?