docs: Add upgrade docs for core #9559

Job	Run time
build_all_features	5m 4s
check	13s
check_clippy	5m 26s
build_default_features (ubuntu-latest)	1m 11s
check_dependencies	51s
build_default_features (macos-latest)	2m 47s
check_docs	4m 31s
check_msrv	3m 20s
build_default_features (windows-latest)	3m 48s
check_website_dependencies	17s
build_all_platforms (ubuntu-latest)	2m 41s
build_under_wasm	45s
build_all_platforms (macos-latest)	3m 31s
build_all_platforms (windows-latest)	4m 39s
unit	4m 34s
	43m 38s

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