feat: add extra_fields to ChainConfig #2050

Job	Run time
doctest	1m 27s
test stable --no-default-features	1m 14s
test stable	1m 11s
feature-checks	2m 56s
test stable --all-features	1m 58s
no-std	23s
test nightly --no-default-features	1m 22s
wasm-unknown	53s
test nightly	1m 13s
wasm-wasi	1m 23s
test nightly --all-features	1m 58s
test 1.76 --no-default-features	35s
cfg-check	31s
test 1.76	52s
clippy	42s
docs	51s
fmt	14s
	19m 43s

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