Add more logging to multi-send endpoints
Add more logging to multi-send endpoints

Summary: Adds a few more log lines to help debug issues with these endpoints.

Test Plan: Relevant tests pass

Reviewers: kav-ya

Reviewed By: kav-ya

Subscribers: jenkins

Differential Revision: https://phab.nylas.com/D2980

closeio/nylas,nylas/sync-engine,nylas/sync-engine,jobscore/sync-engine,jobscore/sync-engine,closeio/nylas,nylas/sync-engine,closeio/nylas,nylas/sync-engine,jobscore/sync-engine,closeio/nylas,jobscore/sync-engine