fix(aws-ecr): add the addToPipeline method to IRepository.

[skinny85]

This is required in order to use the addToPipeline method on imported Repositories.

---

Pull Request Checklist

Please check all boxes, including N/A items:

Testing

• Unit test and/or integration test added
• Toolkit change?: integration tests manually executed (paste output to the PR description)
• Init template change?: coordinated update of integration tests (currently maintained in a private repo).

Documentation

• README: README and/or documentation topic updated
• jsdocs: All public APIs documented

Title and description

• Change type: Title is prefixed with change type:
  • fix(module): <title> bug fix (patch)
  • feat(module): <title> feature/capability (minor)
  • chore(module): <title> won't appear in changelog
  • build(module): <title> won't appear in changelog
• Title format: Title uses lower case and doesn't end with a period
• Breaking change?: Last paragraph of description is: BREAKING CHANGE: <describe exactly what changed and how to achieve similar behavior + link to documentation/gist/issue if more details are required>
• References: Indicate issues fixed via: Fixes #xxx or Closes #xxx

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license.