To allow for richer frontend validations and to align better with the
pajamas design system, I've migrated the new environments form to vue.

I've decided to do a full migration rather than using
`parseRailsFormFields` because I found out about it too late, although
it would have likely been easier.

The form migration is about as bare-bones as possible, no vuex or other
state management, and I use the existing internal API for speed.

Next is to port the Edit Environment form, which is happening separately
as it might involve a little bit of vuex or other state management. As
it is only 2 fields, I suspect it won't, but we will see.

Changelog: changed