Add initial changes for CDN with dedicated WAF plan

[markdboyd]

Related to https://github.com/cloud-gov/private/issues/1098

Changes proposed in this pull request:

• Add new plan for CDN with dedicated WAF plan
• Stub out provision pipeline for CDN with dedicated WAF plan. This pipeline will need more steps added, to be done in follow up PRs
• Stub out update logic for CDN with dedicated WAF plan
• Refactor unit tests that were shared across all plans into new test files with parameterized tests and remove them from original files:
  • tests/integration/test_cdn_provision_common_checks.py
  • tests/integration/test_cdn_update_common_checks.py
• Created library files with shared "subtest" helpers for integration tests:
  • tests/lib/provision.py - shared helpers for all provision tests
  • tests/lib/update.py - shared helpers for all update tests
  • tests/lib/alb/provision.py - shared helpers for ALB provision tests
  • tests/lib/alb/update.py - shared helpers for ALB update tests
  • tests/lib/cdn/provision.py - shared helpers for CDN provision tests
  • tests/lib/cdn/update.py - shared helpers for CDN update tests
• Refactor integration tests to use shared helpers
• Updated docker/docker-compose.yml to allow for easier local testing and running unit tests via VScode

Things to check

• For any logging statements, is there any chance that they could be logging sensitive data?
• Are log statements using a logging library with a logging level set? Setting a logging level means that log statements "below" that level will not be written to the output. For example, if the logging level is set to INFO and debugging statements are written with log.debug or similar, then they won't be written to the otput, which can prevent unintentional leaks of sensitive data.

Security considerations

There should not be any code changes impacting security. However, the ability to provision CDN plans with dedicated WAF web ACLs should be an improvement for security

[bengerman13]

added some comments about type hints, and I think they're a little off in some other places - probably worth running mypy against this codebase in the near-ish future since it's getting a bit big and complex, but I don't think it's a blocker for this PR