Upgrade @gitlab/eslint-config to v2.1.1

What does this MR do?

This upgrades @gitlab/eslint-config to its latest version. This upgrade contains multiple changes that may not have been documented in the package's changelog. Refer to the diff to see all these changes in details: https://gitlab.com/gitlab-org/gitlab-eslint-config/compare/v2.0.0...v2.1.0

To summarize:

• The camelcase rule has been replaced with babel/camelcase
• We added a few plugins:
  • babel: https://github.com/babel/eslint-plugin-babel
  • import: https://github.com/benmosher/eslint-plugin-import
  • @gitlab/i18n
  • @gitlab/vue-i18n
  • no-jquery: https://github.com/wikimedia/eslint-plugin-no-jquery
• We now extend some additional rules sets:
  • plugin:promise/recommended
  • plugin:no-jquery/slim
  • plugin:no-jquery/deprecated-3.4

Due to these changes, ESLint now detects additional errors in GitLab's codebase. These are being addressed in this MR.

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

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