move `fetch metadata` to a separate crate `subxt_utils_fetchmetadata` #5335

Job	Run time
Cargo fmt	8s
Check unused dependencies	25s
Cargo clippy (WASM)	46s
Cargo check	12m 15s
Cargo clippy	3m 17s
Check documentation and run doc tests	7m 16s
Cargo check (WASM)	1m 57s
Test (no_std)	1m 46s
Test (Light Client)	3m 30s
Test (WASM)	12m 6s
Test (Native)	15m 19s
Test chainhead backend	14m 49s
	1h 13m 34s

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