Refactor implementation for set_dhcp

[fabi200123]

This PR updates the current logic of how set_dhcp is being set and used across. Prior to this PR, the implementation used 2 different set_dhcp options, which caused confusion:

osmorphing_info
├── ...
├── nics_set_dhcp
└── osmorphing_parameters
    ├── retain_user_credentials
    ├── ...
    └── set_dhcp

The one from osmorphing_parameters was not implemented by all providers, while the nics_set_dhcp from osmorphing_info is already on all providers (including those that also added the osmorphing_parameters one.

Now, with this PR I have updated the implementation to drop the osmorphing_parameters.set_dhcp option in favor of osmorphing_info.nics_set_dhcp.