Demonstrate how to mock test SeaORM by separating core implementation from the web API

[shpun817]

PR Info

• Closes Demonstrate how to mock test SeaORM's CURD operations on common web APIs #830

Adds

• [x] Demonstration in the Rocket example
  • [x] Take out core implementation into a standalone core crate
  • [x] Write some mock testing with query
  • [x] Write some mock testing with CRUD operations
• [x] Demonstration in the Actix3 example
• [x] Demonstration in the Actix example
• [x] Demonstration in the Axum example
• [x] Demonstration in the GraphQL example
• [x] Demonstration in the Jsonrpsee example
• [x] Demonstration in the Poem example
• [x] Demonstration in the Tonic example
• [x] Demonstration in the Salvo example
• [x] Add workflow job to run the mock tests in the core crate of all examples
• [x] Update the setup instructions in the README.md files

[shpun817]

Hey @billy1624, I thought it'd be easier to just take out the core stuff. I wonder if this structure is good enough for the example, or should I add the api crate and put the rocket code in there?

[shpun817]

@billy1624 Finished transforming the Rocket example!

[billy1624]

Hey @shpun817, @fergus-hou just added an SeaORM example for Salvo. Could we add mock testing to it as well?

• https://github.com/SeaQL/sea-orm/pull/908

[billy1624]

Ohoh, @shpun817 welcome back!

[shpun817]

@billy1624 Ready for review!