Simplify dependency builder in aggregator

[jpraynaud]

Why

The dependency injection builder in the aggregator is too cumbersome and hard to navigate/work with. We need to simplify it for a better maintainability.

What

Split the builder module of the dependency_injection in sub-modules.

How

• Create a sub module for the DependenciesBuilder struct definition
• Create new sub-modules based on the existing modules in the crate (e.g. artifact_builder.rs which builds the dependencies originating from the artifact_builder module) which a new impl block for the DependenciesBuilder

Later

• Have a clear separation between traits and their implementations in the builder
• Use of macros to create the dependency building code?
• Better support of execution environment (test/prod)