Add fetch for categories json on validation

[adamgoth]

Link to Clubhouse story

https://app.shortcut.com/dux-makerdao/story/481/update-categories-in-the-validator-function-for-when-polls-are-created

What does this PR do?

When validating poll markdown (polling/create), this update will now fetch categories dynamically from the community repo. If it fails, it will fallback to the hardcoded categories we have been relying on.

Steps for testing:

Go to polling/create, ensure validation works

Add a GIF:

[shortcut-integration]

This pull request has been linked to Shortcut Story #481: Update categories in the validator function for when polls are created.

[vercel]

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🔍 Inspect: https://vercel.com/dux-core-unit/governance-portal-v2/88fkQKwM5pFLtSnrkhwUQzCgQ7mj
✅ Preview: https://governance-portal-v2-git-chore-sc-481updat-6a2f05-dux-core-unit.vercel.app

[codecov]

Codecov Report

Merging #215 (32be1c3) into develop (f34f561) will decrease coverage by 0.00%.
The diff coverage is 38.46%.

@@             Coverage Diff             @@
##           develop     #215      +/-   ##
===========================================
- Coverage    38.19%   38.18%   -0.01%     
===========================================
  Files           62       62              
  Lines         1605     1608       +3     
  Branches       505      503       -2     
===========================================
+ Hits           613      614       +1     
- Misses         985      987       +2     
  Partials         7        7              

Impacted Files	Coverage Δ
pages/account.tsx	77.41% <ø> (ø)
pages/executive/[proposal-id].tsx	0.00% <ø> (ø)
pages/polling/[poll-hash].tsx	0.00% <0.00%> (ø)
lib/maker/index.ts	31.14% <100.00%> (ø)
pages/polling.tsx	61.45% <100.00%> (+0.40%)	⬆️

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