docs: move `.. code-block::` directives into `docs/examples/` #3247

Job	Run time
mypy	1m 29s
pyright	1m 15s
slotscheck	58s
Test server integration (uvicorn<0.27.0)	1m 1s
Test Minimal Pydantic 1 application	1m 6s
Test Minimal Application with Base Dependencies	48s
Test server integration (uvicorn>=0.27.0)	1m 0s
validate	14s
test-platform-compat	0s
test (3.10) / test	2m 21s
test (3.11) / test	2m 3s
test (3.12) / test	3m 39s
test (3.8) / test	3m 9s
test (3.9) / test	2m 14s
build-docs	0s
upload-test-coverage	17s
codeql	0s
sonar	0s
	21m 34s

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