Snowddl

- Enabled `client_store_temporary_credential` for authenticator `externalbrowser`.

- Added support for serverless alerts. Parameter `WAREHOUSE` for object type `ALERT` is now optional.
- Fixed tests for object type `USER` related to recent changes in output of `SHOW USERS` command.

- Added workaround for `AWS_SNS_TOPIC` DIRECTORY parameter not being present in output of `DESC STAGE` command. It should be possible to use this parameter without triggering `ValueError`.

- Reworked `OUTBOUND_SHARE` resolver. Now it supports more than 3 accounts per share. `SET ACCOUNTS` command was replaced with `ADD ACCOUNTS` and `REMOVE ACCOUNTS`, since `SET ACCOUNTS` no longer supports `SHARE_RESTRICTIONS` parameter.

- Introduced action `validate`. It prepares and validates config, but stops right before connecting to Snowflake. It might be helpful for automated checks and git hooks.
- Removed `self.engine` from application classes. Now engine is created and closed only during `execute()` call, but not during `__init__`.

This change should not have any impact, unless you have custom application classes. In this case replace `with self.engine` call with `with self.get_engine()`. Some output functions now also accept `engine` argument instead of relying on `self.engine`.

- Prevented SnowDDL from trying to change `OWNERSHIP` of Notebook object. This change is explicitly [not supported](https://docs.snowflake.com/en/user-guide/ui-snowsight/notebooks-limitations) by Snowflake.