Support diff mode when using `vyos_firewall_rules`

[sdwilsh]

SUMMARY

This change adds support for diff mode to vyos_firewall_rules. This can aide someone into understanding what will check when using check mode, and can help someone know what has changed when running their play (using just --diff without --check).

ISSUE TYPE

• Feature Pull Request

COMPONENT NAME

vyos_firewall_rules

[sdwilsh]

I'm still interested in getting this change in, for what it's worth.

[gaige]

Hi Shawn. We're in the process of getting things restarted here (I have some PRs that I'm going to be putting in soon as well), having only gotten control of the repository early this week. I'd recommend starting by rebasing on to the current source and checking tests to make sure you've got the baseline working.

I was able to successfully run tests with the final version before the transfer, so I expect it should be working now.

[sdwilsh]

This PR was waiting some design feedback from the previous repo owners because I saw two different paths forward, so I guess I'm looking for your design feedback now.