chore(test): add tests to network utils and validations

[JGAntunes]

What this PR does / why we need it:

Follow up to #2187

See:

• Installer Experience v2 - Milestone 1 #2187 (comment)
• Installer Experience v2 - Milestone 1 #2187 (comment)
• Installer Experience v2 - Milestone 1 #2187 (comment)

We created an interface to allow us to mock and test interactions with the net package.

Which issue(s) this PR fixes:

https://app.shortcut.com/replicated/story/124371/add-tests-to-the-network-methods

Does this PR require a test?

These are tests actually 🙌

Does this PR require a release note?

NONE

Does this PR require documentation?

NONE

[JGAntunes]

This isn't required and will be unreachable since FirstValidIPNet will take care of filtering non ipv4 interfaces, see:

• embedded-cluster/pkg/netutils/ips.go

  Lines 111 to 115 in 6ed500f

  	if ipnet, ok := a.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
  	if ipnet.IP.To4() != nil {
  	return ipnet, nil
  	}
  	}

[github-actions]

This PR has been released (on staging) and is available for download with a embedded-cluster-smoke-test-staging-app license ID.

Online Installer:

curl "https://staging.replicated.app/embedded/embedded-cluster-smoke-test-staging-app/ci/appver-dev-bbd1502" -H "Authorization: $EC_SMOKE_TEST_LICENSE_ID" -o embedded-cluster-smoke-test-staging-app-ci.tgz

Airgap Installer (may take a few minutes before the airgap bundle is built):

curl "https://staging.replicated.app/embedded/embedded-cluster-smoke-test-staging-app/ci-airgap/appver-dev-bbd1502?airgap=true" -H "Authorization: $EC_SMOKE_TEST_LICENSE_ID" -o embedded-cluster-smoke-test-staging-app-ci.tgz

Happy debugging!