* fix(eventstore): differentiate unique constraint error format
* docs: add comment to eventstore vars
* fix(eventstore): return correct error type if unique constraint already exists
(cherry picked from commit f8bf8ea2562b388bbd90debdd86bd551499e9f37)
This implementation increases parallel write capabilities of the eventstore.
Please have a look at the technical advisories: [05](https://zitadel.com/docs/support/advisory/a10005) and [06](https://zitadel.com/docs/support/advisory/a10006).
The implementation of eventstore.push is rewritten and stored events are migrated to a new table `eventstore.events2`.
If you are using cockroach: make sure that the database user of ZITADEL has `VIEWACTIVITY` grant. This is used to query events.
