Draft: chore(deps): update @gitlab/eslint-plugin

What does this MR do?

This updates to @gitlab/eslint-plugin@6, which includes breaking changes via the transitive dependency eslint-plugin-vue being upgraded from v6 to v7.

This adds/improves various lint rules of Vue files; the full changes are documented in their release post. The most notable addition is the vue/no-mutating-props rule, which can help to prevent subtle runtime bugs.

Trivial violations of vue/no-lone-template and vue/order-in-components are fixed in this change, but there are two violations of vue/no-mutating-props that are not trivially fixed, so the rule has been disabled for those to areas of code.

Addresses #1113 (closed), part of &5142.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.