Issue with drift detection with upgrade.force=true

[rsafonseca]

Drift detection only detects drift when the fields managed by the helm-controller are changed.
A user can add additional fields and drift detection will ignore them and won't roll them back.

When upgrade.force=true is set, the replacement strategy is used an all fields not managed by the helm-controller are lost.

This causes an inconsistency in the expected behaviour and can lead to some fields being dropped at an unexpected time after a helmrelease upgrade is triggered.

[stefanprodan]

Fixed by: #822