Other P1/P2 issues

[chpapa]

Description

This is a meta tracking issue for other priority 1 issues:

• Database Hooks param async is reserved word in Python 3.7 py-skygear#196 Database Hooks param async is reserved word in Python 3.7
• All api that accept array of objects should also allow passing array of ids chat-SDK-JS#100 All api that accept array of objects should also allow passing array of ids
• oursky/skygear-cloud#490 Avoid restart of Skygear pod when CMS config updated
• Schema migration is expected to happen after before_save skygear-server#452 Schema migration is expected to happen after before_save

Priority 2:

• Profile Memory Usage for potential memory leaks? skygear-server#560 profile memory usage for memory leak

[carmenlau]

We will plan to do async param update first, as this is one of the features that will have breaking change.