Implement gwctl get namespace

[jongwooo]

What type of PR is this?

/kind feature
/area gwctl
/cc @gauravkghildiyal

What this PR does / why we need it:

Implement gwctl get namespace.

Output Columns	Description	Visibility
NAME	Name of the Namespace
STATUS	Status of the Namespace
AGE	Age of the Namespace
POLICIES	Count of policies affecting this Namespace	-o wide

The -o wide format is not yet implemented, so the column POLICIES is excluded.

Which issue(s) this PR fixes:

Fixes #2854

Does this PR introduce a user-facing change?:

Implement `gwctl get namespace`

[gauravkghildiyal]

/assign

[jongwooo]

The following test failed

It seems that the describe command also needs sorting (by name).

[gauravkghildiyal]

Thanks @jongwooo

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• gwctl/OWNERS [gauravkghildiyal]

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