Add variables command

[enmaboya]

You will probably add variables to the .env one way or another.

This command just simplifies the this process

[gnikyt]

@enmaboya I am fine with this! Maybe the command should be shopify-app:variables:generate? Been looking at how other pkgs do commands, seem to be more along the lines of namespace:section:action.

Approving running the actions too, so we can see test results.

[gnikyt]

Hmm not sure why actions is not showing up for this PR... @Kyon147 have you seen this happen before?

[Kyon147]

@osiset that is strange, we might need to do a blank commit and push in this PR to trigger them. Github might have just had a wobble.

[gnikyt]

@Kyon147 That solved it :/

[gnikyt]

@enmaboya Merged. Maybe add a wiki entry about it if you get time to explain what it does... we probably need a page to explain all commands existing (like this one and webhook) in the future.