cliff has a concept of FormattableColumn which allows CLI implementors
to convert data into human-readable format only when a human-readable
format is requested and keep data unconverted for manchine-readable
formats like JSON or YAML.
Deprecation warnings is now emitted in favor of using FormattableColumn.
Partially implement blueprint osc-formattable-columns
Change-Id: Ia55bc950ecfc666d4a957507beab98eef74390aa
Related-Bug: #1687955