Draft: Update Diffblue CI Integration for GitLab documentation links

What does this MR do and why?

This updates the Diffblue CI Integration on GitLab with more documentation and appropriate links. All changes are purely to visual text and adding of further links. Details shown in screenshots attached.

Related to #435346

Screenshots or screen recordings

Screenshots of UI changes.

Before:

After (changes highlighted in red boxes):

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

To validate the last two boxes open the Diffblue Cover CI Intergration from the Project -> Settings -> Integrations and observe the new docs link when viewing this branch/PR. For the first change, enter a license key (does not have to be valid) and save. When you open the integration again the text will have changed as shown.