fix: add grade.now* events to supported xapi events

[Ian2012]

Description: Describe in a couple of sentences what this PR adds

JIRA: Link to JIRA ticket

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4. If D happened instead - check failed.

Merge checklist:

• All reviewers approved
• CI build is green
• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Commits are squashed

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[bmtcril]

Can you add the docs along with this?

[bmtcril]

👍

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