Omit `NAMESPACE` column when querying resources in a single namespace

[snorwin]

gwctl get always includes the NAMESPACE column in its table output, even when the command explicitly targets a single namespace.

This results in redundant information and reduced readability when working within one namespace.

Example:
Command targeting a single namespace:

$ gwctl get httproute -n example-namespace
NAMESPACE           NAME           HOSTNAMES  PARENT REFS  ACCEPTED  RESOLVED  AGE
example-namespace   route-a        None       1            True      True      51s
example-namespace   route-b        None       2            True      True      51s
example-namespace   route-c        None       1            True      True      51s

Proposed Behavior
Display the NAMESPACE column only when the -A / --all-namespaces flag is specified.

[jongwooo]

/assign