chore(ci): graceful scan-images job execution during grype cdn failures

[saisatishkarra]

Issue

The SCA tool (grype) invoked as part scan-images job downloads the vulnerability DB on each run. This is leading to issues dues to Grype CDN failures sporadically:
Long running jobs failing due to timeout (job resource wastage) when the job is stuck / hung up
Interim solutions to address from multiple fronts:

Summary

• Fixes #140
• Add job timeout for scan job to achieve early graceful job failure
• Ability to bypass scan-images using the vars.DISABLE_SCA_SCAN in the repository variable of emergency when enforcement / fail_build is true. Only Github Admin / Repo Admin access can perform this.
• Bump the scan-actions version to use GH cache as part of [2.4.0](https://github.com/Kong/public-shared-actions/releases/tag/v2.4.0)

Long term solutions:

• The above interim problems Don't work when there first / initial scan job doesn't run until a cache is populated where is long CDN outage. Hence effort to maintain a Kong owned / controlled Grype DB mirror is required.

Effect:

• Default pipeline will be run as-is without any changes when cache / CDN network to populate grype DB succeeds
• when enforcement / input build_fail is false, CVE analysis is skipped
• when enforcement / input build_fail is true, CVE analysis will failed / error the he downstream caller

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix #[issue number]

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