replace JwtSecret type with alloy's

[mattsse]

Describe the feature

alloy now has the same type, which means we can now phase out the reth type:

reth/crates/rpc/rpc-layer/src/jwt_secret.rs

Lines 77 to 79 in 79d505a

	pub struct JwtSecret([u8; 32]);
	impl JwtSecret {

we like need to change the function that reads from disk to a standalone function

Additional context

No response

[quentinv72]

I can do this. @mattsse Would it make sense to define the from_file and try_create methods in alloy directly? As opposed to creating standalone functions in reth.