Feature Request: Jinja Config 'Variables'

[lraithel15133]

It would be cool if we could do expressions such as:

[global_variables]
var_home_current = 1.0

[tmcXXXX stepper_x]
home_current = {var_home_current}

or maybe simply

home_current = var_home_current

The usecase for this is just so you can easily change a single variable in the config (either one thats repeated, or just annoying to access), similar to how you can change gcode variables.