Design and implement CI build system

[jhodapp]

Current CI system for GitHub design requirements:

1. .git commit hook for running mix format
2. Run all Ambi unit tests
3. Run all integration level tests using ambi_mock_client
4. Dependabot integration for dependency security notices
5. Generate a new stable release
   • Able to create/push Docker image to a repo
6. Create predictable assets, e.g. SHA-verifiable image builds
   • Ability to retrigger a build for a given SHA
   • This is likely a separate action

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For the future

1. Build statistics over time (e.g. tracking specific flaky tests)
2. Code coverage, without over-emphasizing this statistic