Support for SecretBinary

[avpjanm]

First of all thanks a lot for this construct!

I am just wondering whether it is possible to create binary secrets. For example key stores.
I kind of got the idea from the readme:

Binary - Just the raw file[...]

But when I tried this it could see some string value of the secret in the console which is not the case for binary secrets.

[markussiebert]

At the moment we use it already for keys, but handle them as 'strings' in the aws call. I agree we should add an option to pass the secret as binary (maybe this should be the default if option binary is used)