feat: add graded boolean to xblock json (FC-0033)

[SoryRawyer]

Description: This PR adds an items graded attribute to the xblock_data_json field and defaults to false if that attribute doesn't exist. This attribute indicates whether the xblock is part of a graded subsection and is a relevant piece of metadata for course problems.

This was discussed in tutor-contrib-aspects issue #292

Testing instructions:

1. Install this branch as part of tutor-contrib-aspects
2. Rebuild images via tutor images build openedx --no-cache
3. Run tutor local do dump-courses-to-clickhouse (possibly with --options "--force" if no courses are pushed)
4. There should now be a graded attribute for some blocks in the xblock_json_data field in event_sink.course_blocks
5. If necessary, generate event data by running the LMS locally and clicking through a course page.

Reviewers:

• tag reviewer
• tag reviewer

Merge checklist:

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

Post merge:

• Create a tag
• Check new version is pushed to PyPI after tag-triggered build is
  finished.
• Delete working branch (if not needed anymore)

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[bmtcril]

Looks good, can you add a test for it and bump the version?

[SoryRawyer]

I think this test follows the appropriate conventions and make validate passes, but please let me know if anything looks off to you.

[bmtcril]

LGTM 👍

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