Add support for S3 custom endpoint with kaniko

[hegand]

/kind feature

Currently fairing does not support custom S3 providers (like minio) with kaniko. There is a PR in kaniko https://github.com/GoogleContainerTools/kaniko/pull/698 that adds support for custom S3 endpoints. It would be great if fairing will support this feature.

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[mojokb]

If minio-context exists as a context builder, it is likely to replace the S3 custom endpoint. I will upload my class as a pull request.

[jtfogarty]

/priority p2 /area engprod