a8n: Render campaign description using markdown

Created by: eseliger

Formatted markdown in detail view

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Created by: codecov[bot]

Codecov Report

Merging #6351 into master will increase coverage by <.01%. The diff coverage is 71.42%.

@@            Coverage Diff             @@
##           master    #6351      +/-   ##
==========================================
+ Coverage   39.19%   39.19%   +<.01%     
==========================================
  Files        1188     1188              
  Lines       60847    60851       +4     
  Branches     5813     5816       +3     
==========================================
+ Hits        23850    23853       +3     
- Misses      34807    34808       +1     
  Partials     2190     2190

Impacted Files	Coverage Δ
web/src/enterprise/campaigns/list/CampaignNode.tsx	0% <ø> (ø)
shared/src/components/Markdown.tsx	100% <ø> (ø)
...rc/enterprise/campaigns/detail/CampaignDetails.tsx	0% <0%> (ø)
shared/src/util/markdown.ts	61.9% <83.33%> (+3.08%)