Clarify help text on Prometheus Integration Page

What does this MR do?

Changes the help text for the Prometheus Service.

Are there points in the code the reviewer needs to double check?

There is usage of HTML in the text.

Why was this MR needed?

The earlier text assumed some familiarity with Prometheus.

Screenshots (if relevant)

How it looks like in GDK:

What are the relevant issue numbers?

Closes #29618 (closed)