Rename "Prometheus" docs section to "Prometheus Server" (#2473)

As per Björn's comment on the team mailing list:

"I think the current "Prometheus" section is not very well named. It is
essentially the part coming from the prometheus/prometheus repo (not
prometheus/docs, as the rest fo the site), and it means "The
Prometheus Server". I think it should be named that way because just
"Prometheus" could mean a lot of things. On prometheus.io,
"Prometheus" mostly refers to the overarching project."

This also adds CSS styles to make sure that the "Prometheus Server" text gets
line-broken in such a way on narrow displays that the second line is indented
correctly.

Signed-off-by: Julius Volz <[email protected]>

Author: juliusv

content/css/docs.css

@@ -311,7 +311,9 @@ footer {
 }
 
 .side-nav .nav-header {
-  display: block;
+  display: flex;
+  gap: 5px;
+  align-items: baseline;
   margin: 20px auto 15px auto;
   font-size: 16px;
 }

content/docs/prometheus/index.md

@@ -1,5 +1,5 @@
 ---
-title: Prometheus
+title: Prometheus Server
 sort_rank: 3
 nav_icon: server
 ---