Update runner settings styling

What does this MR do and why?

The header for the number of available runners was using a h4, which created a disproportion of information where the section was header was just as big as this sub-header. To fix this, we use a h5 and we change the spacing between the headers.

While we are here, we are adding additional description to the runner page according to these designs: #33804[CICD_settings_-_project.png] which adds a header and some info on tags.

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Go to project settings
• Open the runner section
• Notice the new styling

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.