[DEV] Configuration manager

[harvestcore]

Summary: Design and implement a service to handle all the configuration variables.

Functional notes:

• The service must be simple to use, with simple methods to get or set configuration variables from different sources.

Technical notes:

• Ideally, a Get and Set method must exist.
• The configuration variables may come from the environment.
• The configuration variables may come from the appsettings.json file.
• The service must be created in the resources project, so it is accessible by the other projects.

Dependencies:

• None for now.

Subtasks:

• None for now.

Acceptance criteria:

• Unit tests are added if possible.
• The technical notes are met.