0.7.0 release (launchbadge#2575)

* WIP preparing 0.7.0 release

* fix: re-enable examples

* fix doctests in `sqlx-core`

* cherry-pick CHANGELOG entry for 0.6.3

* add actions workflow for examples

* fix(cli): close connection after running migrations

* fix examples

* fix(sqlite): fix parsing of URLs via `Any`

* fix(example): don't let Postgres `listen` example run forever

* fix Postgres `transaction` example