meshery: [mesheryctl] improve the error messages shown to users for "mesheryctl app"

Description: Improve the error messages in mesheryctl commands from the user’s perspective. Commands in scope of this issue: mesheryctl app, mesheryctl app onboard, mesheryctl app offboard, mesheryctl app list, mesheryctl app view

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We need to make sure of the following things

• There are proper error messages when users
  • Give more arguments to a command than required
  • Misspell a command
  • Do not give the required input via flags or args
  • Use the command without any arguments or flags.
• The error messages being displayed to users are meaningful from user’s perspective. And if applicable, a potential fix for the problem should be shown too. For example
  • “failed to unmarshal response body” could be modified to “couldn’t process JSON response from server”
  • “manifest not found” could be modified to “manifest not found. Please provide the path to the app manifest.”

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📚 For the Reference head over to this pr.