[tests] Unify test utils of authority

[asonnino]

We currently have a bunch of test utilities to spawn new authorities (with or without initial objects) scattered around the codebase. a few examples:

sui/sui_core/src/unit_tests/authority_tests.rs

Line 1357 in 2960c00

fn init_state_parameters() -> (Committee, SuiAddress, KeyPair, Arc<AuthorityStore>) {

sui/sui_core/src/unit_tests/authority_tests.rs

Line 1379 in 2960c00

async fn init_state() -> AuthorityState {

sui/sui_core/src/unit_tests/authority_tests.rs

Line 1404 in 2960c00

pub async fn init_state_with_objects<I: IntoIterator<Item = Object>>(objects: I) -> AuthorityState {

These utilities are not only useful for `authority_tests.rs', they are also re-used in other test files. It would be nice to regroup them all in the crate called 'test-utils'.