Move `internal/entities/properties` to `pkg`

[JAORMX]

Properties are leveraged by many pieces of Minder, including providers. It should be considered a public API instead of being in our bloated internal package.

The idea is to move properties to pkg. However, we should leave the underlying service package as internal, as it's a minder-server implementation detail.

Ideally, it would move to something like pkg/entities/properties

[letsmakecakes]

I can do this work

[JAORMX]

@letsmakecakes sounds good! I'll assign you. Thanks for working on this!