Add firewall support (orphan mode and normal mode). Add unit tests.

[patrickdappollonio]

Description

This PR:

• Adds support for firewall checks. Each firewall has a few parameters in the API that show how many other resources depend on it (see below)
• Adds unit tests for pretty much every possible combination
• Makes orphan deletions sequential instead of parallel for easy reading of the output

To verify a firewall is "orphan", we get the count in use for instance, cluster, and loadbalancer. If all 3 are zero, then it's a leftover.

  {
    "id": "415164c0-40ab-4ee5-b92e-768b93bcbcb0",
    "name": "example-a211-9e20a7",
    "account_id": "96eda81a-7a36-4a89-ad4a-69ae28e216a5",
    "rules_count": 6,
    "instance_count": 0,
    "cluster_count": 0,
    "loadbalancer_count": 0,
    "default": "false",
    "label": "",
    "network_id": "464ff5e7-9807-430b-8e1c-22c12414382c",
    "rules": []
  },

Related Issue(s)

Fixes #

How to test