Salt path options are now global and default to None.
Salt path options are now global and default to None.

Since we now evaluate each `salt.syspath` entry one by one, we only set
the passed settings in the generated `_syspaths` module.

The default values will mandate unless explicitly overridden in the
setup stage.

Refs #19157, #19160, #19161
Fixes #19514
Closes #19515

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt