EE: Adds EE folder in the stylelint command

What does this MR do?

1. Adds EE folder in the stylelint command
2. Fixes the failures from stylelint in the EE folder. Failures were:

FAILURES:

ee/app/assets/stylesheets/pages/groups.scss
   ✖   string-quotes 16:15   Expected single quotes (string-quotes)
   ✖   string-quotes 21:15   Expected single quotes (string-quotes)
   ✖   string-quotes 26:15   Expected single quotes (string-quotes)

ee/app/assets/stylesheets/pages/pipelines.scss
   ✖   declaration-block-trailing-semicolon 154:44   Expected a trailing semicolon (declaration-block-trailing-semicolon)

ee/app/assets/stylesheets/pages/roadmap.scss
   ✖   function-parentheses-space-inside 8:39   Unexpected whitespace after "(" (function-parentheses-space-inside)
   ✖   function-parentheses-space-inside 11:30   Unexpected whitespace before ")" (function-parentheses-space-inside)
   ✖   function-parentheses-space-inside 13:42   Unexpected whitespace after "(" (function-parentheses-space-inside)
   ✖   function-parentheses-space-inside 16:35   Unexpected whitespace before ")" (function-parentheses-space-inside)
   ✖   function-parentheses-space-inside 18:41   Unexpected whitespace after "(" (function-parentheses-space-inside)
   ✖   function-parentheses-space-inside 21:30   Unexpected whitespace before ")" (function-parentheses-space-inside)
   ✖   function-parentheses-space-inside 363:39   Unexpected whitespace after "(" (function-parentheses-space-inside)
   ✖   function-parentheses-space-inside 368:10   Unexpected whitespace before ")" (function-parentheses-space-inside)
   ✖   function-parentheses-space-inside 372:39   Unexpected whitespace after "(" (function-parentheses-space-inside)
   ✖   function-parentheses-space-inside 377:10   Unexpected whitespace before ")" (function-parentheses-space-inside)
   ✖   string-quotes 148:12   Expected single quotes (string-quotes)
   ✖   string-quotes 232:18   Expected single quotes (string-quotes)
   ✖   string-quotes 246:14   Expected single quotes (string-quotes)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #10938 (closed)