Relax course offering version keys

[bethanyaconnor]

A small PR to prepare for all of our assignable scripts to have a course offering and version. My plan is to create course offerings with the same name as the script, such as 20-hour. As this has a number, it fails the course offering key validation. These scripts also don't have a year associated with them so I'm planning on having the course version key either be their name or "unversioned" (I'm still deciding on this), so I relaxing that validation in this PR as well.

I modeled both of these on the resource key validation, so I don't think it will break any markdown syntax but definitely let me know if there's something I should check for.

PR Checklist:

• Tests provide adequate coverage
• Privacy and Security impacts have been assessed
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[davidsbailey]

thank you for breaking these changes down like this.