Migrate to firewall ID in infrastructure status without provider ID encode/decode

[Gerrit91]

During our research regarding provider IDs, we came across the infrastructure status firewall ID field, where we translate the firewall ID into a provider ID (metal:///<partition-id>/<firewall-id>).

This is completely unnecessary in this context and can lead to confusion. It should be possible to simply set this fields to the firewall ID and remove the encode/decode part.

To make this happen, we need to migrate the existing fields. So, at the start of the reconciliation we have to check whether the field is encoded or not and save the plain id in the status instead.