feat: container app vulns by default

[yaronschwimmer]

• [X] Follows CONTRIBUTING rules

What does this PR do?

Enables container app scan by default. We are introducing a new flag, exclude-app-vulns in case a user would like to disable app scan.

How should this be manually tested?

snyk container test <image_with_app> should return app scan results without additional parameters. snyk container test --exclude-app-vulns <image_with_app> should return only operating system scan results.

Any background context you want to provide?

What are the relevant tickets?

https://snyksec.atlassian.net/browse/MYC-56