Update css-loader ^1.0.0 -> ^2.1.1

What does this MR do?

Update css-loader node module to new upstream major version,

Breaking changes: https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md#breaking-changes-1

Notes: https://github.com/webpack-contrib/css-loader/releases/tag/v2.0.0

katex module needs css-loader 2.x to build and we'd like to use same version for gitlab as well in debian.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability 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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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• 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