Lint against outdated docs links rendered with `HelpPageLink`

What does this MR do and why?

Lint against outdated docs links rendered with HelpPageLink

This adds a local ESLint rule to ensure documentation links rendered with the HelpPageLink Vue component are up-to-date.

This follows up on !159149 (merged) where we added an ESLint rule to catch outdated links generated with the helpPagePath Js helper. This basically does the same checks, but for the HelpPageLink component which is itself a wrapper around helpPagePath.

This also fixes the two violations this new rule found:

• In ecfe7f28, the Change the linked namespace title was changed to Change the linked group in doc/subscriptions/gitlab_com/index.md, breaking an anchor link in the UI.
• In c8dd4a4d, the Delayed refresh section was moved from doc/user/usage_quotas.md to doc/user/packages/container_registry/reduce_container_registry_storage.md, breaking a link in the UI.

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