add extraKey to useRpcEndpoint

[Zetazzz]

Luca found getter in useQuery(['rpcEndpoint', getter], can only be serialized as a null. So there's no difference between multi-chain endpoints, when switching between chains things wouldn't be changed automatically. So Luca suggested adding an extra key for better react query usage, like:

export const useRpcEndpoint = <TData = string | HttpEndpoint>({
    getter,
    options,
    extraKey
}: UseRpcEndpointQuery<TData>) => {
...useQuery(['rpcEndpoint', getter, extraKey],
}

[pyramation]

Would be nice to use a better option name, besides that LGTM!

[Zetazzz]

I reconsidered this.

I removed flag. If user left extraKey null, the behavior of the function remain the same query key as before('["rpcEndpoint",null]'). If user input an extraKey, user will get '["rpcEndpoint", "extraKey"]'.

[Zetazzz]

There's a requirement from @marslavish :
some of customized hooks should have extraKey too. So I added needExtraQueryKey option in ReactQuery option, but currently, only useEndpoint is changed into this logic. I'll make another PR on other customized hooks.