[FEATURE REQUEST] Vault: Allow to configure AppRole auth mount path

[lkubb]

Is your feature request related to a problem? Please describe.
Currently, Salt assumes the configured AppRole uses the default mount path at auth/approle. Vault allows to mount backends to customizable paths though, which is not supported by the current implementation.

Describe the solution you'd like
Be able to configure the AppRole mount path Salt authenticates at.

Describe alternatives you've considered
Use the default one only for Salt

Additional context
#62684