Expand session server configuration example

Darren Eastmanrequested to merge
DarrenEastman-main-patch-64ad into main

What does this MR do?

Update content in the Global section of the Runner Advanced Configuration document

Why was this MR needed?

Documentation review and update for KR 8511](https://gitlab.com/gitlab-com/gitlab-OKRs/-/issues/8511)

What are the relevant issue numbers?

#37933 (closed)

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