Switch snowplow storage strategy back to localStorage pending upstream fix

In https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8461 we switched back to snowplow's default stateStorageStrategy (which is cookie) as a temporary fix for a Javascript error described in https://gitlab.com/gitlab-org/gitlab-ee/issues/8111.

When snowplow's has released the fix, we should switch back to stateStorageStrategy: "localStorage"

The following discussion from !8461 (merged) should be addressed:

• @wortschi started a discussion:

  Once snowplow has released the fix, we should switch back to stateStorageStrategy: "localStorage"