feat: add plain summary mode for completeness report generation #53

Job	Run time
integration (none, json, dummy)	19s
integration (repo-10, json, online)	15s
integration (repo-basic, xml, online)	15s
integration (repo-10, xml, online)	27s
integration (none, xml, dummy)	20s
integration (repo-basic, json, online)	17s
	1m 53s

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