use namespace name instead of uuid for flags

[strantalis]

When creating a new attribute I expected the ability to pass in the namespace by name but get the following error.

go run main.go --insecure --log-level debug --host https://nightly.platform.io policy attributes create --name test -s opentdf.io -r ANY_OF -v value1 -v value2

Failed to create attribute: rpc error: code = InvalidArgument desc = invalid input syntax for type uuid

[jrschumacher]

Blocked by opentdf/platform#1300