refactor: add missing information to data classes

[mariajgrimaldi]

Description:
In this PR, a new event was introduced with its data classes, but it was missing two changes
that are being added here.

• Add ordering field to DiscussionTopicContext
• Add more context to class arguments

Testing instructions:
Follow test instructions in this PR.

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)

[JuanDavidBuitrago]

I test and the result was great!!!

[felipemontoya]

Given that this was something that broke the CI at edx-platorm and not here, I think we should be doing something to make the CI in this repo catch that kind of error. Is this a realistic possibility?

[mariajgrimaldi]

@felipemontoya we could try and maintain some tests here in sync. That would give us some reassurance on how the event is being used (the send_event with some dummy data). What do you think?

[mariajgrimaldi]

I'll merge this PR and add a POC of tests for the events definitions.