docs: integrate Vale for documentation linting (#2242)

* added value rules

* resolved errors raised by vale

* added github action

* fixes to github action

* added details in contribution guidelines

* added rule for numbers

* limited checks to errors

docs/styles/docs/Gender.yml

@@ -0,0 +1,7 @@
+extends: existence
+message: "Don't use '%s'."
+level: error
+ignorecase: true
+tokens:
+  - he/she
+  - s/he