perf: Cache installationId lookup in ParseClient.buildHeaders#1

AdrianCurtin wants to merge 3 commits into

chadpav:pr/send-installation-idchadpav/Parse-SDK-Flutter:pr/send-installation-idfrom

AdrianCurtin:cache-installation-idAdrianCurtin/Parse-SDK-Flutter:cache-installation-idCopy head branch name to clipboard