Add Ember instance types for DANDI CLI

[asmacdo]

This should not merge until these endpoints actually exist, but may be helpful to the Ember team to have this as a draft anyway.

By adding an ember instance type (and ember-staging), the DANDI CLI should be able to be used as-is rather than requiring a custom PyPI.

#1517
#1527

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.32%. Comparing base (ba384c6) to head (a60e2b2).

❗ There is a different number of reports uploaded between BASE (ba384c6) and HEAD (a60e2b2). Click for more details.

HEAD has 95 uploads less than BASE

Flag	BASE (ba384c6)	HEAD (a60e2b2)
unittests	96	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1565       +/-   ##
===========================================
- Coverage   88.36%   68.32%   -20.05%     
===========================================
  Files          78       78               
  Lines       10735    10720       -15     
===========================================
- Hits         9486     7324     -2162     
- Misses       1249     3396     +2147     

Flag	Coverage Δ
unittests	68.32% <ø> (-20.05%)	⬇️

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