feat(pencil): Add ability to fail admission on missing sidecar configmap

[mvaalexp]

:pencil: Description

• Add ability to fail admission on missing sidecar configmap

:pencil: Customer Notes

• https://github.com/ExpediaGroup/kubernetes-sidecar-injector/issues/55
• sidecar-injector.expedia.com/skipOnMissingSidecar: true/false

:heavy_check_mark: Checklist

• [x] Semantic Versioning present in commit message.

Semantic Versioning

1. fix(pencil): patches a bug (PATCH); e.g., fix(pencil): fixed a bug
2. feat(pencil): new feature (MINOR); e.g., feat(pencil): added a feature
3. BREAKING CHANGE/perf(pencil): footer BREAKING CHANGE:, breaking change (MAJOR); e.g., perf(pencil): api change

[mvaalexp]

Need to deploy and test and update README, leaving in draft.