Custom env variable

[jimafisk]

Currently some of the config set in plenti.json can be referenced in the magic env prop available at the top-level /layouts/global/html.svelte of your project:

• env.baseurl
• env.local
• env.entrypointHTML
• env.entrypointJS
• env.cms.repo
• env.cms.redirectUrl
• env.cms.appId
• env.cms.branch

I wonder if it makes sense to reserve env for custom key/values and instead pull defined settings out of a new variable called config:

• config.baseurl
• config.local
• config.entrypointHTML
• config.entrypointJS
• config.cms.repo
• config.cms.redirectUrl
• config.cms.appId
• config.cms.branch
• config.env.myCustomKey <-- User defined under env key in plenti.json
• config.env.myCustomKey2 <-- Same

Most projects allow for a .env file, but since we allow individual builds per environment (e.g. local / dev / stg / prod / etc.. per #183) using plenti.json config files, I think it makes the most sense to require that we define them there.

To avoid introducing a breaking change we could keep env and using a subcategory of custom or something instead. Would like to emphasize the best naming over backwards compatibility though.