✨ Add support for shared/top-level parameters (dependencies, tags, etc) (#2434)
* ✨ Add Default and DefaultPlaceholder data structures
to handle defaults and overrides
* ✨ Add utils to get values by priority handling DefaultPlaceholders
* ✨ Add support for top-level parameters in FastAPI, APIRouter, include_router
including: prefix, tags, dependencies, deprecated, include_in_schema, responses, default_response_class, callbacks
* ♻️ Update openapi utils to handle DefaultPlaceholder for response_class
* 📝 Update bigger-application example code to use top-level params
and showcase them in APIRouter, FastAPI, include_router
* 📝 Update docs for Bigger Applications, include diagrams, top-level params
* 🔥 Simplify code and docs for callbacks as default_response_class is no longer required
* 📝 Add docs for top-level dependencies, in FastAPI()
* 📝 Add docs reference to top-level dependencies in docs for decorator
* ✅ Update/increase tests for Bigger Applications including shared parameters
* ✅ Add tests for top-level dependencies in FastAPI()
* ✅ Add tests for internal DefaultPlaceholder
* ✅ Update/increase tests for callbacks with top-level parameters
* ✅ Add LOTS of tests covering branches and cases for shared parameters
in top-level FastAPI, path operations, include_router, APIRouter, its path operations, nested include_router, nested APIRouter, and its path operations
* 🎨 Format/reorder parameters for consistency in FastAPI, APIRouter, include_router
