chore:volto 16 in tests, update docs, fix stylelint overrides

Makefile

@@ -97,12 +97,12 @@ stylelint:		## Stylelint
 
 .PHONY: stylelint-overrides
 stylelint-overrides:
-	$(NODE_MODULES)/.bin/stylelint --syntax less --allow-empty-input 'theme/**/*.overrides' 'src/**/*.overrides'
+	$(NODE_MODULES)/.bin/stylelint --custom-syntax less --allow-empty-input 'theme/**/*.overrides' 'src/**/*.overrides'
 
 .PHONY: stylelint-fix
 stylelint-fix:	## Fix stylelint
 	$(NODE_MODULES)/stylelint/bin/stylelint.js --allow-empty-input 'src/**/*.{css,less}' --fix
-	$(NODE_MODULES)/.bin/stylelint --syntax less --allow-empty-input 'theme/**/*.overrides' 'src/**/*.overrides' --fix
+	$(NODE_MODULES)/.bin/stylelint --custom-syntax less --allow-empty-input 'theme/**/*.overrides' 'src/**/*.overrides' --fix
 
 .PHONY: prettier
 prettier:		## Prettier

RELEASE.md

@@ -20,55 +20,55 @@ You need to first install the [release-it](https://github.com/release-it/release
    ```
    npm install -g release-it
    ```
-   
+
 Release-it uses the configuration written in the [`.release-it.json`](./.release-it.json) file located in the root of the repository.
-   
+
 Release-it is a tool that automates 4 important steps in the release process:
 
 1. Version increase in `package.json` ( increased from the current version in `package.json`)
 2. `CHANGELOG.md` automatic generation from commit messages ( grouped by releases )
 3. GitHub release on the commit with the changelog and package.json modification on the develop branch
 4. NPM release ( by default it's disabled, but can be enabled in the configuration file )
 
-To configure the authentification, you need to export GITHUB_TOKEN for [GitHub](https://github.com/settings/tokens) 
+To configure the authentification, you need to export GITHUB_TOKEN for [GitHub](https://github.com/settings/tokens)
 
    ```
    export GITHUB_TOKEN=XXX-XXXXXXXXXXXXXXXXXXXXXX
    ```
- 
+
  To configure npm, you can use the `npm login` command or use a configuration file with a TOKEN :
- 
+
    ```
    echo "//registry.npmjs.org/:_authToken=YYYYYYYYYYYYYYYYYYYYYYYYYYYYYY" > .npmrc
    ```
 
 #### Using release-it tool
-  
+
 There are 3 yarn scripts that can be run to do the release
 
 ##### yarn release-beta
 
-Automatically calculates and presents 3 beta versions - patch, minor and major for you to choose ( or Other for manual input). 
+Automatically calculates and presents 3 beta versions - patch, minor and major for you to choose ( or Other for manual input).
 
 ```
-? Select increment (next version): 
-❯ prepatch (0.1.1-beta.0) 
-  preminor (0.2.0-beta.0) 
-  premajor (1.0.0-beta.0) 
-  Other, please specify... 
+? Select increment (next version):
+❯ prepatch (0.1.1-beta.0)
+  preminor (0.2.0-beta.0)
+  premajor (1.0.0-beta.0)
+  Other, please specify...
 ```
 
 ##### yarn release-major-beta
 
 Same as `yarn release-beta`, but with premajor version pre-selected.
-    
+
 ##### yarn release
 
 Generic command, does not automatically add the `beta` to version, but you can still manually write it if you choose Other.
 
 #### Important notes
 
-> Do not use release-it tool on master branch, the commit on CHANGELOG.md file and the version increase in the package.json file can't be done without a PULL REQUEST.  
+> Do not use release-it tool on master branch, the commit on CHANGELOG.md file and the version increase in the package.json file can't be done without a PULL REQUEST.
 
 > Do not keep Pull Requests from develop to master branches open when you are doing beta releases from the develop branch. As long as a PR to master is open, an automatic script will run on every commit and will update both the version and the changelog to a production-ready state - ( MAJOR.MINOR.PATCH mandatory format for version).