Related issues/epics empty state update

From #354769 (closed). On the issue detail and epic detail page, update the related items component:

Remove the info icon and link, and add copy to the body of the widget with context on use case. Add a learn more link within this copy that links out to the docs page that the info icon previously linked to.

Solution

Show Free users:

Link issues together to show that they're related. Learn more.

Show Premium+ users:

Link issues together to show that they're related or that one is blocking others. Learn more.

Show Ultimate users:

Link epics together to show that they're related or that one is blocking others. Learn more.

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Reminder for implementation that we now want to add aria-role to Learn more. links: https://design.gitlab.com/usability/helping-users/#learn-more

So, here, they'd be:

Learn more about linking issues.

Learn more about linking epics.

Docs Support

For issues requiring an update to GitLab docs, please note that this is part of the definition of done for this issue. Please create a separate MR for the docs update related to the MR for the actual change to ensure code reviews are not blocked by TW reviews.

• This issue requires an update to GitLab docs
• This issue does not require an update to GitLab docs