Change link to generate service ping help doc

What does this MR do and why?

Changes location of help link to "generate service ping" console command from rails cheat sheet to service ping development page following docs update in #367388 (closed).

The original link still exists, but the rails cheat sheet page could be deleted at any time (as it now only contains links to other pages) so this change will protect against a 404 error if that happens.

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