Add integration tests for Cassandra `INSERT .. IF NOT EXISTS` queries

[rukai]

These queries rely on LWTs and also return the existing data in the response, which is different to regular INSERTs which return nothing.
As such, they are a potential edge case where bugs could exist.
We should add integration tests to cover `IF NOT EXISTS when used directly on native types as well as when used on lists, sets and maps.

I suggest implementing a new function insert_if_not_exists in each of the following files and call that files insert_if_not_exists after the insert function, here:

shotover-proxy/shotover-proxy/tests/cassandra_int_tests/native_types.rs

Lines 119 to 121 in d316e8b

	insert(session).await;
	select(session).await;
	run_query(session, "DROP KEYSPACE test_native_types_keyspace").await;

shotover-proxy/shotover-proxy/tests/cassandra_int_tests/collections/list.rs

Lines 94 to 98 in d316e8b

	pub async fn test(connection: &CassandraConnection, driver: CassandraDriver) {
	create(connection).await;
	insert(connection).await;
	select(connection, driver).await;
	}

shotover-proxy/shotover-proxy/tests/cassandra_int_tests/collections/set.rs

Lines 78 to 82 in d316e8b

	pub async fn test(connection: &CassandraConnection, driver: CassandraDriver) {
	create(connection).await;
	insert(connection).await;
	select(connection, driver).await;
	}

shotover-proxy/shotover-proxy/tests/cassandra_int_tests/collections/vector.rs

Lines 43 to 47 in d316e8b

	pub async fn test(connection: &CassandraConnection) {
	create(connection).await;
	insert(connection).await;
	select(connection).await;
	}

shotover-proxy/shotover-proxy/tests/cassandra_int_tests/collections/map.rs

Lines 118 to 122 in d316e8b

	pub async fn test(connection: &CassandraConnection, driver: CassandraDriver) {
	create(connection).await;
	insert(connection).await;
	select(connection, driver).await;
	}