Initial implementation

[chris-okuda]

Scope of changes

Initial implementation which was copied and modified from Envoy.

• Changed the Configure function to be Initialize and take the config AND templates
• Added configs for the important backoff options so the user can control timing
• using our x/backoff implementation instead of an external package that was used in Envoy
• setup an example template for the live email test under testdata/

Type of change

• bug fix
• new feature
• documentation
• testing
• other (describe)

Acceptance criteria

No special requirements.

Author checklist

• I have manually tested the change and/or added automation in the form of unit tests or integration tests
• I have updated the dependencies list
• I have added new test fixtures as needed to support added tests
• I have added or updated the documentation
• Check this box if a reviewer can merge this pull request after approval (leave it unchecked if you want to do it yourself)

Reviewer(s) checklist

• Any new user-facing content that has been added for this PR has been QA'ed to ensure correct grammar, spelling, and understandability.
• To the best of my ability, I believe that this PR represents a good solution to the specified problem and that it should be merged into the main code base.