* Release 3.0.0

* No alpha or rc wording

* Move dox_auth, dox_openapi and dox_validation to their own repos

The dox repo and dox-orm depended on each other: dox_auth needs
dox_orm, and dox_orm needs dox_annotation and dox_validation. So
neither repo could be released first.

Now the dependencies go one way only:
natives -> dox-validation, dox-openapi -> dox -> dox-orm -> dox-auth.

- dox_auth, dox_openapi and dox_validation move to dartondox/dox-auth,
  dartondox/dox-openapi and dartondox/dox-validation, with their
  history. The package names and APIs stay the same, so apps change
  nothing.
- dox_core no longer has dox_orm as a dev dependency. The tests of
  @Unique, @Exists and closing the database on stop move to dox-orm.
- CI clones the new repos. ci/use-siblings.sh (was use-sibling-orm.sh)
  makes the workspace use the dox_openapi and dox_validation clones.
- RELEASING.md gives the release order.

* dox_builder tests: read dox_validation through the package config

The tests read dox_validation's source with a path next to dox-builder.
dox_validation has its own repo now, so that path is gone. Find it
through the package config instead, as a dev dependency.

* Template smoke test: the CLI uses the local packages too

The CLI took its dependencies from pub.dev. In a release, the new
versions (like dox_migration) are not there yet, so the test failed on
every release PR. Now the CLI gets the same overrides as the app. The
published versions are checked by pub publish and the steps after the
release.