fix(db-postgres): allow to clear select fields with `hasMany: true`

[r1tsuu]

What?

Previously, using Postgres, select fields with hasMany: true weren't clearable. Meaning, you couldn't pass an empty array:

const updatedDoc = await payload.update({
  id,
  collection: 'select-fields',
  data: {
    selectHasMany: [],
  },
})

Why?

To achieve the same behavior with MongoDB.

How?

Modifies logic in packages/drizzle/src/upsertRow/index.ts to include empty arrays.