Prevent display of meta-properties, update runtime-images schema

[kevin-bates]

The addiitional meta-properties printed on each help message have been removed and the runtime-image schema's image_name property description has also been updated. I've kept the ability to enable them via a boolean since it was trivial to do and might be useful.

Fixes #837

$ elyra-metadata install runtime-images --schema_name=runtime-image
'--name' is a required parameter.

Install a metadata instance into namespace 'runtime-images'.

Options
-------

--replace
	Replace existing instance
--schema_name=<string>
	The schema_name of the metadata instance to install
--name=<string>
	The name of the metadata instance to install
--display_name=<string>
	The display name of the Runtime Image
--description=<string>
	The description of this Runtime Image instance
--image_name=<string>
	The image name (including optional tag)

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[akchinSTC]

LGTM, merging