feat: Terms of service page

[nellh]

Implements #2609 to make terms for both upload and downloads referenced in one place. Content is shared from the components that display this information.

[codecov]

Codecov Report

Attention: Patch coverage is 86.27451% with 14 lines in your changes missing coverage. Please review.

Project coverage is 43.09%. Comparing base (b990ddb) to head (2b71fa2).
Report is 9 commits behind head on master.

Files	Patch %	Lines
...ackages/openneuro-components/src/footer/Footer.tsx	0.00%	8 Missing ⚠️
packages/openneuro-app/src/scripts/routes.tsx	0.00%	2 Missing ⚠️
...p/src/scripts/uploader/upload-disclaimer-input.tsx	0.00%	2 Missing ⚠️
packages/openneuro-server/src/handlers/sitemap.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3122      +/-   ##
==========================================
+ Coverage   42.68%   43.09%   +0.41%     
==========================================
  Files         593      596       +3     
  Lines       37780    37840      +60     
  Branches     1094     1095       +1     
==========================================
+ Hits        16125    16306     +181     
+ Misses      21447    21327     -120     
+ Partials      208      207       -1     

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