Return inventory as json in the standalone server mode

[demeringo]

Problem

When run in standalone "server" mode, cloud-scanner only returns metrics.

There is no way to get the inventory as json (API like).

Solution

Add a server route that allow to retrieve inventory (as json).

Alternatives

Additional context or elements

• This feature only exist today when cloud scanner is deployed as a serverless app / lambda function.
• I see more and more use cases where cloud scanner is deployed as a docker container and I miss this feature in this context.

[demeringo]

Implemented by #305