feat: Improve namespace validation logic and enhanced inspect output

[opjt]

related issue #3851

@AkihiroSuda

changes

fixes

• Added validation to require the --label flag for the update command.
• Added namespace existence checks to both the update and inspect commands.
  • (inspect) If non-existent namespaces are included, a warning log is now emitted.
    • this logic is based on the behaviorvolume-inspect

features

• Enhanced namespace inspect output:
  • Added Containers information (count, ids)
  • Added Images information (count, ids)
  • Added Volumes information (count, names)
• The inspect command now provides the same level of information available in namespace list.

[Shubhranshu153]

NIT: Squash the commits. (Probably 2 commits, one for the feature and one for the fix)

[opjt]

@AkihiroSuda When you have time, could you please take a look at this PR?