Add --properties-separator option (#1951)

This commit adds the --properties-separator option, which lets users
specify the separator used between keys and values in the properties
output format. This is done by adjusting the value of
github.com/magiconair/properties#Properties.WriteSeparator at encode
time.

Some refactoring of the properties encoder unit tests was done to make
it easier to write unit tests that include different separator values.

Fixes: #1864

Signed-off-by: Ryan Drew <ryan.drew@isovalent.com>

pkg/yqlib/operator_encoder_decoder.go

@@ -14,7 +14,7 @@ func configureEncoder(format PrinterOutputFormat, indent int) Encoder {
 	case JSONOutputFormat:
 		return NewJSONEncoder(indent, false, false)
 	case PropsOutputFormat:
-		return NewPropertiesEncoder(true)
+		return NewPropertiesEncoder(true, ConfiguredPropertiesPreferences)
 	case CSVOutputFormat:
 		return NewCsvEncoder(ConfiguredCsvPreferences)
 	case TSVOutputFormat: