NETOBSERV-223: filter by empty names

[mariomac]

Allows filtering by empty string names.

This PR doesn't include searching by empty IP.

[jpinsonneau]

Should it manage empty port ? Currently the frontend doesn't allow empty / ""

Also the same with Protocol. I'm not sure if we should manage them or not 🤔

[jpinsonneau]

Tested and works fine with namespaces / name / kind / owner name / node name

[mariomac]

@jpinsonneau I see. The original task definition was talking about Kube metadata (text) but it's true that we could extend it to any other field type, like IPs or numbers. If we agree to do it also for other field types, we could do it into another PR so we do it more incremental.

[openshift-ci]

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