Use link_to helper instead of interpolated links

What does this MR do and why?

Use link_to helper instead of interpolated links

related to: #419672 (closed)

Screenshots or screen recordings

Before	After
<a href="/help/administration/custom_project_templates.md">Learn more</a>	<a href="/help/administration/custom_project_templates.md">Learn more</a>
<a href="/help/user/packages/package_registry/supported_functionality#deleting-packages">What are the risks?</a>	<a href="/help/user/packages/package_registry/supported_functionality#deleting-packages">What are the risks?</a>
<a href="https://gitlab.com/groups/gitlab-org/-/epics/10415">epic 10415</a>	<a href="https://gitlab.com/groups/gitlab-org/-/epics/10415">epic 10415</a>
<a href="/help/administration/settings/continuous_integration#required-pipeline-configuration">What is a required pipeline configuration?</a> <a href="/help/administration/settings/instance_template_repository">How do I create an instance template repository?</a>	<a href="/help/administration/settings/continuous_integration#required-pipeline-configuration">What is a required pipeline configuration?</a> <a href="/help/administration/settings/instance_template_repository">How do I create an instance template repository?</a>

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.