Explain how Jira issue prefixes work

What does this MR do?

I had a misunderstanding on how the Jira issue prefixes work. I thought the prefix was actually part of the Jira issue ID (kind of like a non-regex way to match the issue IDs). Bojan cleared up my misunderstanding in #413906 (comment 1455303167)

When I read our current docs - the way the prefix works isn't as clear which is where my initial misunderstanding came from. Let's improve the docs with an example on how the Jira issue prefix works.

Related issues

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