Add (branch) scope to non-secret variables

[MikeShepard]

Summary of the new feature / enhancement

As a user, I want to be able to set the value for a non-secret variable for different branches in my development environment.

Then, when I push the changes, the variable will be set to the "production" value when git syncs.

As it is, I either have to push the dev value to prod, or use the database as the variable repo, or use a secret. All 3 scenarios involve either a variable not being set in prod or having the dev value in prod until I override it.

Proposed technical implementation details (optional)

Allow multiple branch/value-pairs for the value of a variable.

The variable is set to the value corresponding to the branch in the git settings.