Improve basic repo architecture

[elfkuzco]

Rationale

Improve basic repository structure with stub implementations of features. This resolves #14

Changes

• Set up working FastAPI server
• Count list of mirrors on backend startup
• Make database migrations on backend startup
• Set up a worker manager that sleeps at intervals after doing a dummy task
• Set up a working docker compose for development
• Add workflow to publish docker images
• Combine QA for all subprojects into one workflow and separate jobs using dorny/paths-filter

[rgaudin]

Thank you ;

Please see inline comments ;

Also please use meaningful names for you branches and dont reuse the same one always.

On the dev compose, this can be a future task, but we've seen that those static docker images are not that practical and it's more convenient to use tweaked images that mount the project root and run fastapi in dev mode (reload). Allows having everything docker-setup (like the DB) but still have the convenience of hot-reload.

[rgaudin]

Good!
Regarding workflows, please use the Github action filter directly.

[rgaudin]

LGTM now!