AWS ECR Remote Hashing

[sberss]

Description

This change adds AWS ECR remote hashing support, which helps fix call caching for jobs using AWS ECR hosted containers. This change supports both private and public ECR registies.

There were a couple non-standard behaviours from ECR which have been mitigated in this PR:

• Private ECR requires Basic authentication. The ability to override the authorization scheme for a particular registry was added.
• ECR does not return a Docker-Content-Digest header, so a fallback to calculate the image digest from the response body has been added.
• ECR supports images with no repository e.g. 123456790.dkr.ecr.eu-west-2.amazonaws.com/foo.

Release Notes Confirmation

CHANGELOG.md

• I updated CHANGELOG.md in this PR
• I assert that this change shouldn't be included in CHANGELOG.md because it doesn't impact community users

Terra Release Notes

• I added a suggested release notes entry in this Jira ticket
• I assert that this change doesn't need Jira release notes because it doesn't impact Terra users