Create pullup resolution method on average opponent ranking

[tienne-B]

From the WSDC Power Pairing Procedures:

3.7 If possible, the team which is ‘pulled-up’ to a bracket shall be the team from the bracket immediately below whose opponents from all the preliminary rounds which have already been completed have the lowest average rank in the preliminary round league tables heading into current round (or the available team whose opponents have the lowest average rank on the league table subject to the other provisions within these guidelines).

Currently, we do not support this, as it depends on team standings while our current restrictions only include metrics, so without having been "windowed." We could run a full standings generator within standings/teams.py to create this new "metric."