Adds PC only Revision Invitation for single-blind venues

[purujitgoyal]

[codecov[bot]]

Codecov Report

Merging #1356 (330ca22) into master (5ac2826) will increase coverage by 0.04%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1356      +/-   ##
==========================================
+ Coverage   72.10%   72.15%   +0.04%     
==========================================
  Files          26       26              
  Lines        8260     8271      +11     
  Branches     1478     1481       +3     
==========================================
+ Hits         5956     5968      +12     
  Misses       1932     1932              
+ Partials      372      371       -1     

Impacted Files	Coverage Δ
openreview/conference/builder.py	80.25% <100.00%> (+0.08%)	:arrow_up:
openreview/conference/invitation.py	88.97% <100.00%> (+0.11%)	:arrow_up:

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[melisabok]

Good idea, how should we call the invitation?

PCs should sign the revision using the PC group only.

UPDATE: in this case we should enable this invitation for all the venues, single and double blind

[melisabok]

This is added to the API 2 venues