Deprecate the old announcements endpoint

The old announcements endpoint has been deprecated in favour of the more recent corporate actions endpoint. The new endpoint offers more structured response (different schema for each corporate action type) and better overall data quality.

The version of the new endpoint has been increased from v1beta1 to v1. This means that we now promise backward compatibility guarantee for the endpoint: we will not introduce breaking changes. The previous v1beta1 version can still be used, so no migration is required if you've already been using the endpoint.