Snowflake AWS_SNS_TOPIC for External Tables

[Brendon-Wood13]

Description & motivation

Currently run_operation stage_external_sources does not allow the optional config of a AWS_SNS_TOPIC in the creation of external tables. This change adds an optional parameter aws_sns_topic to the Snowflake plugin that formats the Create External Table command in the Snowflake format seen here tables-external-s3

Checklist

• [x] I have verified that these changes work locally
• [x] I have updated the README.md (if applicable)
• [x] I have added an integration test for my fix/feature (if applicable)

[github-actions[bot]]

This PR has been marked as Stale because it has been open with no activity as of late. If you would like the PR to remain open, please comment on the PR or else it will be closed in 7 days.

[github-actions[bot]]

Although we are closing this PR as stale, it can still be reopened to continue development. Just add a comment to notify the maintainers.

[corleyscotte]

@dataders @jtcohen6 Is this PR still something we can consider adding into the project?