Add label filtering (-l) for get namespaces

[deszhou]

What type of PR is this?

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #2913

Does this PR introduce a user-facing change?:

Add label filtering (-l) for get namespaces

➜  gwctl get namespaces -l kubernetes.io/metadata.name=monitoring
NAME        STATUS  AGE
monitoring  Active  29d

[k8s-ci-robot]

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[deszhou]

➜ gwctl get ns -l kubernetes.io/metadata.name=envoy-gateway-system
Unrecognized RESOURCE_TYPE

The command gwctl get namespaces is currently supported by gwctl, yet the shorthand gwctl get ns is not available, should we add ns as a shorthand to facilitate its use by users?

[gauravkghildiyal]

➜ gwctl get ns -l kubernetes.io/metadata.name=envoy-gateway-system
Unrecognized RESOURCE_TYPE

The command gwctl get namespaces is currently supported by gwctl, yet the shorthand gwctl get ns is not available, should we add ns as a shorthand to facilitate its use by users?

Yes definitely, lets do it in the same PR.

[deszhou]

@gauravkghildiyal done, I'd like to continue working on Add label filtering (-l) for describe commands

[gauravkghildiyal]

/label tide/merge-method-squash

[gauravkghildiyal]

Thanks @yeedove

/ok-to-test
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gauravkghildiyal, yeedove

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