Code improvements (tooling, async...)

[raphodn]

Story

For the v1 we went a bit fast, here is a list of known improvements :

• schema: add field descriptions (pydantic) & examples
• background tasks: avoid passing db (see this discussion)
• tests: teardown data between each test, add more tests
• tests: use PostgreSQL instead of SQLite
• documentation: improve it (ex: docker), add docstring
• ci: upgrade release-please to v4

[teolemon]

We could add automatic client library generation: https://github.com/marketplace/actions/generate-client-library-w-the-openapitools-generator

[kundan-bhardwaj]

@raphodn I am a newbie in opensource and want to fix this issue can you please elaborate this in detail.