Add ExcludeInterfaceRegexp to Net Dev monitor

[mmiranda96]

What does this PR do?

As a solution for #659, this PR adds field ExcludeInterfaceRegexp to network device monitor. This field is used to stop tracking metrics for certain network interfaces.

This change also edits config net-cgroup-system-stats-monitor.json to exclude Calico interfaces (according to this doc, cali and tunl interfaces) and veth, which are interfaces created dynamically and only add noise to the metrics.

Additionally, I refactored the code in order to make it more testable and added some unit tests.

How to test this change?

1. Create a Kubernetes cluster that uses Calico (I personally used GKE and followed instructions here). Ensure the cluster uses the new NPD version and config (in my case, I manually copied the binaries and config to the node).
2. Run some workload, trigger new network interfaces creation, and ensure metrics are not being reported for Calico interfaces.

[mmiranda96]

/cc @bobbypage

[bobbypage]

Change LGTM, a few small nits about the test. Thanks for adding the the exclude feature and test coverage, it's a big improvement!

[mmiranda96]

Addressed your comments @bobbypage. Thanks for the review!

[bobbypage]

Thanks!

/lgtm

/assign @Random-Liu

[Random-Liu]

@vteratipally Could you take a look at this change? Thanks!

[vteratipally]

@mmiranda96 Did you happen to check if adding the filter improving the time reporting the metrics

[mmiranda96]

@vteratipally I didn't check that specifically, I just ensured that metrics are properly filtered.

[vteratipally]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bobbypage, mmiranda96, vteratipally

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