feat: Add private dataset alert to snapshots for dataset admins

[effigies]

This attempts to be DRY by pulling out the warning that is shown on the draft when a dataset has snapshots and is private into a DatasetAlertPrivate component. This is then added to the snapshot page if the dataset is private and the user is an admin.

Closes #3331.

[codecov]

Codecov Report

Attention: Patch coverage is 87.80488% with 5 lines in your changes missing coverage. Please review.

Project coverage is 48.16%. Comparing base (4048ed5) to head (ed34c4c).
Report is 16 commits behind head on master.

Files with missing lines	Patch %	Lines
...uro-app/src/scripts/dataset/snapshot-container.tsx	60.00%	4 Missing ⚠️
...nneuro-app/src/scripts/dataset/draft-container.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3332      +/-   ##
==========================================
+ Coverage   47.32%   48.16%   +0.84%     
==========================================
  Files         595      595              
  Lines       38033    38055      +22     
  Branches     1261     1298      +37     
==========================================
+ Hits        18000    18331     +331     
+ Misses      19846    19546     -300     
+ Partials      187      178       -9     

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