Improve ITP Onboarding Sprint 1 GitHub Workshop

A few things I noticed which could be better:
- [x] Labels in the repo aren't relevant to the repo - I've updated these
- [ ] We should pre-label more issues
- [ ] We should override the issue categories so that when someone creates a new issue it's not so curriculum-focused
- [ ] We should cover in the workshop that sometimes issue fields have placeholders, and we want to remove them - a lot of issues got filed with `` at the start
- [ ] We should blank out the PR template because it's not relevant in this task (or add one that is)
- [ ] Add two learning objectives: "Create a pull request" and "Interpret and act on bot comments on a pull request"