feat(firewall): add `applied_to_resources` property

[phm07]

Fixes #660

[phm07]

I'll implement the property in the CLI as we so we can check if it works

Edit: See https://github.com/hetznercloud/cli/pull/1082

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 79.19%. Comparing base (1ff862d) to head (f16a92f). Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #667      +/-   ##
==========================================
+ Coverage   79.08%   79.19%   +0.11%     
==========================================
  Files          50       50              
  Lines        4413     4413              
==========================================
+ Hits         3490     3495       +5     
+ Misses        706      703       -3     
+ Partials      217      215       -2     

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