ui: page/route generation through elm-land CLI

[plyr4]

Description

with go-vela/ui#761 merged in, we moved a lot closer to being able to use the elm-land CLI to generate boiler plate code for new pages and routes. some more work is required, but it seems doable.

• fork https://github.com/elm-land/elm-land/tree/main/projects/cli
• modify the generation scripts to work with our /src/elm/ file structure
• modify the templates to retain support for our opinionated boiler plate fixes.
• refactor the UI code to work with the modified elm-land generate command

[plyr4]

started working on a fork of the elm-land CLI that takes does a couple specific things:

• takes src/elm project structure into account
• skips generation for Main.elm
• applies the OSS license to all files

so far so good! it helped me generate the code changes in go-vela/ui#779

[plyr4]

one outstanding issue is the CLI wants to have a 1:1 relationship between pages and routes, so elm-land generate is overwriting the "alias routes" like <org>/<repo>/pulls because theres no specific page file for it... we could create a page file for each one? not too bad, but its going to be messy/hacky either way IMO