Proposal: Wire for dependency injection

[ondrej-fabry]

This PR introduces new way to do dependency injection for the cn-infra application components (plugins). It uses github.com/google/wire library to generate code for connecting the components. This encourages explicit initialization at compile-time instead of using magic to resolve dependencies during runtime. Here's guide for the wire library: https://github.com/google/wire/blob/master/docs/guide.md

By switching to this method we could dramatically improve the Ligato code-base:

• make the application setup much more readable to users
• remove the requirement of defining Init()/AfterInit()/Close() methods
• the "plugin" concept could become obsolete
  • packages agent and infra could be removed
  • the boiler-plate files options.go could be removed
  • various cn-infra components could be used separately
• make the actual program initialization much faster (no reflection)
• help catch dependency-related issues during compilation instead of panic at runtime

[sonarcloud]

SonarCloud Quality Gate failed.

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3.3% Duplication