chore: add shorthand flag for image option in generate command

[lekaf974]

Description

fIX #272

What does this PR do?

Add -i shorcut for generate command

  -i, --image string                    An optional container image to use for any container with image == '.'

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• New chore (expected functionality to be implemented)

Checklist:

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• I've signed off with an email address that matches the commit author.

[mathieu-benoit]

LGTM