Snowddl

- Added more tests for `TABLE` and `VIEW` object types.
- Improved project description.

- Implemented `EXTERNAL FUNCTION` object type.
- Added validation for YAML config file names for object types supporting overloading.
- Re-create "invalid" `EXTERNAL TABLES` automatically.
- Switched test account to AWS.

- Reworked parsers. Now most exceptions raised in parsers will no longer interrupt the program, but will be stored and reported later. Each reported exception now has a proper traceback and pointer to file which most likely caused the problem.
- Implemented [placeholders](https://docs.snowddl.com/basic/yaml-placeholders) in YAML configs.
- Config path is now fully resolved prior to execution, which should help to produce consistent logs regardless of symlinks or cwd.
- Added support for `STAGE FILE` object type, which is intended mainly for packages for Snowpark functions.
- Added support for Snowpark function options: `IMPORTS`, `HANDLER`, `RUNTIME_VERSION`.

- Use `SYSTEM$BOOTSTRAP_DATA_REQUEST` to detect edition of Snowflake account.
- Drop admin role with prefix when calling `destroy` action with `--env-prefix`. Current role of connection reverts to original role without prefix.

- Added `NETWORK_POLICY` and `RESOURCE_MONITOR` to list of supported object types.

- Added `is_sandbox` for `DATABASE` object type, in addition to `SCHEMA` object type.
- Dump empty `params.yaml` files for `DATABASE` and `SCHEMA` during conversion to preserve empty schemas. Empty directories cannot be pushed to Git.
- Added basic safety checks for `env_prefix`. It cannot contain double underscore `__` and it cannot end with underscore `_`.