fix: events track experiment variation

[MaxFrank13]

This PR adds a property to every event that references which variation the user has been bucketed in the Skills Builder.

This also adds a new event to the CareerInterestCategorizinator that will fire whenever a user clicks on the dropdown menu. There is also a new edx.skills_builder.viewed event that fires as soon as the application loads.

Minor update: "Coding Instructor" did not have any related skills so it's been removed.

[codecov-commenter]

Codecov Report

Merging #69 (19f160f) into main (445b365) will decrease coverage by 18.52%.
Report is 35 commits behind head on main.
The diff coverage is 52.18%.

@@             Coverage Diff             @@
##             main      #69       +/-   ##
===========================================
- Coverage   91.59%   73.08%   -18.52%     
===========================================
  Files          30       43       +13     
  Lines         369      587      +218     
  Branches       68      133       +65     
===========================================
+ Hits          338      429       +91     
- Misses         30      150      +120     
- Partials        1        8        +7     

Files	Coverage Δ
src/index.jsx	0.00% <ø> (ø)
src/skills-builder/SkillsBuilderContextWrapper.jsx	100.00% <100.00%> (ø)
...r/skills-builder-context/SkillsBuilderProvider.jsx	100.00% <ø> (ø)
...lls-builder/skills-builder-context/data/actions.js	100.00% <100.00%> (ø)
...s-builder/skills-builder-context/data/constants.js	100.00% <100.00%> (ø)
...lder/skills-builder-header/SkillsBuilderHeader.jsx	87.50% <100.00%> (+4.16%)	⬆️
...c/skills-builder/skills-builder-header/messages.js	100.00% <ø> (ø)
...lls-builder/skills-builder-steps/data/constants.js	100.00% <100.00%> (ø)
...rc/skills-builder/skills-builder-steps/messages.js	100.00% <ø> (ø)
...er-steps/select-preferences/CareerInterestCard.jsx	100.00% <100.00%> (ø)
... and 32 more

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[cdeery]

This is fine for now, but the next time we add a variation, we will have to go through and make a bunch of changes. We should think about abstracting the sendAction to a wrapper function that that can determine the variant, because that one flag might not always be the distinguishing feature