class defined as "Ping" but endpoints trying to fetch "Pings"

[cjbaezilla]

Title
Fix typo in user guide documentation first api page

Description
Class was defined as "Ping" but endpoints were pointing to "Pings" returning 404 in the example.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[mergeable]

Hi there, cjbaezilla! 👋

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