[6CORE-077] Add reactive database support for Shopping Cart Service

[andrey-kiyas]

• For time being we are going to use postgres for this service, but replace with NoSQL database in future
• We need to set up library for persistent logic
• We need to provide kick-off configurations, e.g. database url, password and so on
• We need to code the entity model regarding ER diagrams
• Be align with Reactive Approach
• Consider using the same username/password for all services, e.g. username=postgres and password=postgres

[kateryna-mykh]

@andrey-kiyas , dependency to reactive-postges-persistent should be only in infra pom.