Allowing for custom vale config

[rkratky]

Currently, we check for the existence of vale.ini and only run get_vale_conf.py if it isn't found. That means it's cumbersome to have a custom vale.ini in the repo: one needs to modify both the Makefile (remove the check for vale.ini) and the script that fetches the vale config (add a check for vale.ini, so it's not overwritten).

I propose to default to a behavior that would run get_vale_conf.py regardless of vale.ini presence and only fetch vale.ini if it doesn't exist already.

(Use case: custom vale severity settings (warning vs error).)

[SecondSkoll]

Change made in #333