[WIP] Add difficulty tracks filter for activities

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Difficulty Tracks</issue_title>
<issue_description>We are having freshmen and senior students attending the same activities. While this makes sense for several things, some people have started asking for intermediate and advanced level activities.

Recommendation

Create an optional parameter for all activities that indicates the difficultly level. For now this will be 3 levels:

• Beginner
• Intermediate
• Advanced

If the field is not provided for an activity, it is for all levels. It should not be displayed on the card.

• Add a filter in the left side bar. It should have the 3 above levels and an "All option" that only show activities with no specified difficulty information.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Difficulty Tracks #6

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