Api match mds schema

[tacaswell]

Tests pass, but we do not have a doct conda package it can see yet.

[tacaswell]

@arkilic @danielballan In metadataservice the events are stored with data/timestamp as two dictionaries. In this implementation (and previously) they are stored as a (value, timestamp) tuple in a single data dict.

Pros of changing schema (now)

• already doing a migration, so this is a great time to do it if we are going to do it
• store on disk matching the in-memory representation
• reduces thrashing on both way in and out

cons of changing schema

• store in form that matches read, however that data gets re-formatted on the way out of bs to the {data:{}, timestamp: {}} form.
• current schema help to enforce that we always have value + timestamp.

On net, I think changing the schema now is the better option.

[ghost]

Agreed. Less migrations :+1: