aws-ecr: add page

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• The page (if new), does not already exist in the repo.
• The page is in the correct platform directory (common/, linux/, etc.)
• The page has 8 or fewer examples.
• The PR title conforms to the recommended templates.
• The page follows the content guidelines.
• The page description includes a link to documentation or a homepage (if applicable).

For #5653

[258204]

I included some commands where the base command involves a different application, but illustrates how ecr interacts with them. Most of these are adapted from here: https://docs.aws.amazon.com/AmazonECR/latest/userguide/getting-started-cli.html

[bl-ue]

Minor.