Use `timestamp with time zone` for timestamp fields in `projection_versions`

[datafoo]

The timestamps inserted_at and updated_at in projection_versions table use the PostgreSQL type timestamp without time zone.

Since inserted_at and updated_at are to be implicitly interpreted as UTC, why not making it explicit and use the PostgreSQL type timestamp with time zone instead?

[slashdotdash]

I'm unsure why I chose to use timestamp without timezone for these fields, possibly because I thought NaiveDateTime was more appropriate than DateTime.

Am happy to accept a pull request to change these.

[datafoo]

I may work on this pull request.