Fix HTTP Server errors

[mostafa]

Ticket(s)

• Graceful shutdown #439

Description

This PR fixes two bugs:

1. The gRPC client in the HTTP server used to use a context with cancel, and it was refactored to add graceful stop functionality, hence the function now returns an http.Server instead. This causes the defer to be called to cancel the context, hence a closed gRPC client will be received by the gateway, which produced HTTP 499 with the message: grpc: the client connection is closing.
2. The previous code was using koanf, which was causing marshaling issues. Now the already unmarshaled struct is used.

Related PRs

• Add graceful shutdown for grpc server and http server #490

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