Summary: Filter push down fix that included added an extra stopping condition for push down ( if parent.children().size() > 1 ) and moving the rule into the optimizer

Test Plan: tested in optimizer and seems to work, previously failing query works as well

Reviewers: nserrino, jamesbartlett, #engineering

Reviewed By: nserrino, #engineering

Differential Revision: https://phab.corp.pixielabs.ai/D4914

GitOrigin-RevId: fa2f9fc4bb02ead7cf8b50831710aa261fb01d2e