Add lint rule for PF5 SCSS/CSS

[SanjalKatiyar]

Ref: https://www.patternfly.org/get-started/upgrade#review-and-update-variable-and-class-names

Need to investigate whether we can add rule(s) to prevent addition of any class, variable, mixin, function names with a pf- prefix (only allowed prefixes should be pf-v5- and pf-m). This is to make sure no PF4 SCSS/CSS is added by mistake.