mmlid: Add migration to convert timestamp to timestamptz

[dirkmc]

I noticed that in postgres we are using the TIMESTAMP type.
We should instead be using TIMESTAMPTZ to account for time zone differences.

We should add a migration to convert from TIMESTAMP to TIMESTAMPTZ type.
It's not necessary to convert existing rows to the correct timezone because they will over-written the next time the piece doctor gets to that piece (usually within 24 hours).