Adjust ENV variables to follow vite rules

[grzanka]

          > This is my `.env` file:

ubuntu@yap-dev:~/ui$ cat .env
# BEGIN ANSIBLE MANAGED BLOCK
REACT_APP_BACKEND_URL = https://yap-dev.c3.plgrid.pl:8443
REACT_APP_ALT_AUTH = plg
REACT_APP_KEYCLOAK_BASE_URL = https://sso.plgrid.pl
REACT_APP_KEYCLOAK_REALM = PLGrid
REACT_APP_KEYCLOAK_CLIENT_ID = yap-dev.c3.plgrid.pl
# END ANSIBLE MANAGED BLOCK

does it need adjustment ?

VITE_ before any variable e.g. VITE_REACT_APP_BACKEND_URL

Originally posted by @NiEkOKsU in yaptide/ui#1696 (comment)