use of the word unknown for default values

[ptdropper]

Default values are assigned to the value "unknown" for input arguments. Review this feature for possible change if necessary.

[jkowalleck]

all thse switches are optional, right, and they default to 'unknown'.

cyclonedx-buildroot/cyclonedx_buildroot/_internal/cli.py

Lines 154 to 163 in e242718

	parser.add_argument('-i', action='store', dest='input_file', default='manifest.csv',
	help='comma separated value (csv) file of buildroot manifest data')
	parser.add_argument('-o', action='store', dest='output_file', default='buildroot_IOT_sbom',
	help='SBOM output file name for json and xml')
	parser.add_argument('-n', action='store', dest='product_name', default='unknown', help='name of the product')
	parser.add_argument('-v', action='store', dest='product_version', default='unknown', help='product version string')
	parser.add_argument('-m', action='store', dest='manufacturer_name', default='unknown',
	help='name of product manufacturer')
	parser.add_argument('-c', action='store', dest='cpe_input_file', default='unknown',
	help='cpe file from make show-info')

having all thse "unknown' in an SBOM, especially in optional fields and properties - makes no sense.