Add sfutils skills: PAT, External Volume, Network Rule

[sfc-gh-ksampath]

Summary

• Adds three new Cortex Code skills for Snowflake infrastructure automation:
  • programmatic-access-token — Create and manage Snowflake PATs for service accounts
  • external-volume — Create and manage external volumes with AWS S3 for Iceberg/data lake
  • network-rule — Create and manage network rules and policies for IP-based access control
• Each skill includes: SKILL.md with standardized metadata, CLI reference, manifest flows, replay flows, supplemental docs, and a Python CLI entrypoint
• All skills use a TOML manifest (.sfutils/manifest.toml) for state tracking and reproducibility

NOTE: These are fresh, purpose-built skills — not migrations from Snowflake-Solutions. They were written from scratch for the Cortex Code skill platform with its metadata format, interactive workflow patterns, and CLI-driven architecture.

Test plan

• Verify each skill loads correctly via $programmatic-access-token, $external-volume, $network-rule
• Confirm SKILL.md frontmatter validates against the skill catalog schema
• Test CLI entrypoints (pat, vol, nw) respond to --help
• End-to-end: run a dry-run workflow for each skill against a test Snowflake account

.... Generated with Cortex Code