Build users service with spring native (#6813)

[quinarygio]

To make it work on my ubuntu I had to install an additional library: sudo apt-get install zlib1g-dev

To build a native image of users service: cd services/users

gradle clean build

gradle nativeCompile

gradle bootBuildImage

Issues to be invetigated:

• configuration proprties are taken ONLY from application.yml, so I had to copy configuration from common.yml and users.yml
• JacksonConfig objectMapper bean was not instantiated correctly, so I removed it