Support float[] for Postgres

[schauder]

As pointed out in #1037 (comment) float arrays don't work properly with Postgres.

This is actually a two part problem.
One is that writing doesn't work because Postgres requires a special type representation, when writing arrays of floats.
That issue will be resolved by 9f0ada5
The other problem is that loading that array again results in a List of double instead of float.

[ctailor2]

When defining the column in postgres, if float4[] is used for the data type instead of float[] or float8[], the postgres jdbc driver returns the expected List<Float> rather than List<Double>. See the jdbc driver array support documentation for details on the postgres data type to java type mapping.

While this works natively for postgres jdbc driver, other stores may not have a data type mapping to java Float (i.e. hsql), so it would still be better to try to convert array elements to match the expected entity type, if possible.