Multiple docs links in release post entry description

Why is this change being made?

Related to: gitlab-org/gitlab#250030 (closed)

If multiple doc links were provided, the first would always win. This would cause unexpected output if a link was included inline in a paragraph and then a dedicated documentation link is provided below.

Now the doc link will only be detected from a line with one link, where the link is at least 70% of the content of the line. This will prevent inline links being detected incorrectly.

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.