Minimum age requirement

[mplsmitch]

**What problem does your proposal solve?

I'm doing this PR on behalf of @marius-at-atb in in Trondheim, Norway. Additional discussion can be found in #771 . They have a need for a field to contain a minimum age requirement in order to use a vehicle. There are potentially a number of user requirements that could be included in the vehicle_types file, such as a drivers license, helmets etc but until we have real-world use cases my preference is to limit this to a single field that contains minimum age. In the future if there are additional needs beyond age we could develop a list of enums.

If anyone has additional needs in this area I'd like to hear from you so we can include them before this goes to a vote.

What is the proposal?

This PR adds a single field min_age to vehicle_types.json. The field is OPTIONAL and defined as a non-negative integer that describes the minimum age required to use the vehicle.

This is a non-breaking change that would be included in the next minor version release scheduled for November.

Is this a breaking change?

• [ ] Yes
• [x] No
• [ ] Unsure

Which files are affected by this change?

vehicle_types.json