[mod add] flag style

[Bechma]

Instead of relying on static skeletons with hardcoded names, it will be a better idea to have a flag system:

• --api for a new module with API capabilities
• --host for a new module with Rest Host capabilities
• --background for a new module with background template
• --db for a new module with database capability

The idea is to have the ability to mix them, so, if I want a new module with api and database: --api --db, If I just want api and background --api --background etc

For now blocked until cyberfabric/cf-template-rust#15 resolved