Remove --stdin flag from core commands

[kaduartur]

What would you like to be added:
I would like to remove the necessity to use the --stdin flag in the core commands.

Core commands:

• add
• completion
• create
• delete
• init
• list
• set
• show
• update
• build
• upgrade
• tutorial
• metric

Why is this needed:
to facilitate the use of Ritchie with stdin

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