Approve new style R2 ad units

R2 ad units will now have the same format as NextGen. However, the new
units must now be approved manually too.
Tighten ad unit filter to 4 segments

Domain/section/contenttype/platform
Merge remote-tracking branch 'origin/master' into supportR2InAdUnitApprovalApp
Merge branch 'master' into supportR2InAdUnitApprovalApp
Merge pull request #5461 from guardian/supportR2InAdUnitApprovalApp

Support r2 in ad unit approval app