Handle non string value

[johnraz]

This PR contains 2 main changes:

1. Give more context when a secret is not found, here the JSON unmarshalling error was swallowed and we were only seeing "secret no found". It was really hard to diagnose and I actually had to do this change and recompile to find out what the issue was.
2. While amazon secrets manager usually holds only string as secret value we ended up with integers in some places... automatically created by amazon RDS... I changed the code so that any type would be unmarshalled properly and then converted to a string. It's more flexible than failing completely to load the all secret map.

I'm not a Gopher so I apologize in advance for any wrong doing ;-)

[CLAassistant]

All committers have signed the CLA.

[tboerger]

Using interface everywhere feels at least for me wrong, IMHO the json paarser should make sure everything is a string.

[johnraz]

Hello @tboerger,

I'm not sure to understand what you are proposing?

Do you mean it should keep erroring if aws-secrets sends back non string values?
Or do you mean the conversion should happen earlier and a string should be passed down the stack after the parser has done its job?

Thanks for you time and feedback.