docs: add code migration guides for v1.3.1 and v1.4.0, update v1.4.0 migration guide #1398

Job	Run time
build	6m 43s
deploy-argocd	12s
devshell-tests (nixos)	20s
deploy-rustdoc	0s
devshell-tests (macos)	45s
local-environment-tests	6m 20s
local-environment-tests-post-merge	0s
upload-chain-specs	0s
local-environment-tests-post-merge-alert	0s
post-merge-actions-complete	0s
argocd-tests	0s
teardown-argocd	0s
local-environment-tests-alert	5s
pre-merge-checks-complete	1s
	14m 26s

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