Integrate lerna

[setaman]

@DaTebe, @anatoliynovo

This PR brings massive refactoring to our core services and introduces lerna as a management tool for the dependencies. I'll give a brief introduction here. The details will be captured in the docs.

• You have to use lerna for dependency management and linking to local common packages.
  Install lerna globally with npm i -g lerna or use it through npx lerna ...

• lerna manages packages in a sub directory (/packages by default), core/services/ in our case. Therefore, lerna config file and package.json are located in core/. ⚠️So the working directory for lerna commands is core ⚠️

• To install all dependencies run lerna bootstrap --hoist. This command installs deps for all services and hoists common packages in core/node_modules.
  For specific service run lerna bootstrap --hoist --scope=<service-name>

• To add a dependency: lerna add <package-name> [--scope=<service-name>]

• To remove node_modules: lerna clean [--scope=<service-name>]

• ⚠️ npm commands like install will fail as @diva/common package is not in any registry now

• To run the service you can use lerna or just normally execute the npm scripts

So what has changed:

• Repeatedly written code has been moved to @diva/common. These includes express server setup, JSON schema validation, Kafka messages validation and messaging in general, connections with Mongo and Elasticsearch, CRUD operations on entities and other frequently used utilities. These modules were rewritten to be flexible and generalized as possible.
• ESLint configuration has been moved to @diva/eslint-config. All service use this config
• Code base of the services reduced by 40-60%
• Dockerfile's now have 2 stages: bootstrap the app with lerna and build executable binary, copy and execute binary.
• Docker images size reduced 145 -> 85 MB

We need a strong testing and debugging on this as many things have changed and i have not tested every single endpoint yet.