Snowflake Apps: resolve deploy defaults from config table

[sfc-gh-gbloom]

Pre-review checklist

• I've confirmed that instructions included in README.md are still correct after my changes in the codebase.
• I've added or updated automated unit tests to verify correctness of my new code.
• I've added or updated integration tests to verify correctness of my new code.
• I've confirmed that my changes are working by executing CLI's commands manually on MacOS.
• I've confirmed that my changes are working by executing CLI's commands manually on Windows.
• I've confirmed that my changes are up-to-date with the target branch.
• I've described my changes in the release notes.
• I've described my changes in the section below.
• I've described my changes in the documentation.

Changes description

snow __app deploy now reads fallback defaults from SNOW_APPS.CONFIG.APP_DEFAULTS (keyed by role) when values like warehouse, compute_pool, and eai aren't set in snowflake.yml. It's valid for the table to be missing, empty, or inaccessible.

Resolution order:

1. snowflake.yml
2. config table
3. built-in defaults