[ECS] [request]: Support privately signed CA's for ECS fargate tasks pulling from private registries

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**Tell us about your request**
For a fargate task if you are pulling from a private repository either allow you to point at an ACM certificate ARN or pass in the public cert for verification of the endpoint of the image pull

**Which service(s) is this request for?**
ECS Fargate and potentially ECS EC2

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
In our corporate environment we are not allowed to have public facing applications and such all of our VPC's are private and all CA Certificates are signed by a non-public Internal CA. This presents a problem for corporate customers myself because we cannot tell Containerd/The Docker Daemon to trust a root/intermediate certificate at all when trying to pull from our internal container repository with an internally signed CA

Related Issues:
- #740
- #98

**Are you currently working around this issue?**
We are currently not working around this issue but looking for possible solutions. One possibility is pushing to ECR but the issue with this is the images need to go cross account and ECR currently presents itself as a heavy handed solution to solve for a problem we can solve with our private internal container repository

**Additional context**
If this functionality cannot be implemented within short time period the documentation should at least be updated for the following link to say that only container registries with publicly signed CA certificates are supported at this time because this missing functionality was not found out till the container deployment solution was created.
Relevant Links: https://docs.aws.amazon.com/AmazonECS/latest/developerguide/private-auth.html

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

Start with the private-auth documentation linked in the issue and review related issues #740 and #98 to understand the current ECS Fargate limitations. Done would mean either supporting privately signed CA certificates for private registry image pulls or updating the documentation to state that only publicly signed CAs are supported.

Written by the indexing model from the issue text.