create docker image

[albertrdixon]

Story details: https://app.shortcut.com/gladly/story/169699

What

• Create Dockerfile for building simple migrate image
• Add Github Actions workflow for building and pushing the image to github container registry

Testing

• Once built and pushed, pull and run the image with

docker run --rm -ti ghcr.io/sagansystems/migrate --help

[saganbot]

Story	https://app.shortcut.com/gladly/story/169699
Review Guide	https://www.notion.so/gladly/Change-Approvals-at-Gladly-37814c3e0da8411985f6a1adaa2f64ad
Rollback	For repos on weekly release: roll back the release. For repos on continuous deployment (CD): revert the code change and deploy.

[saganbot]

Code review checklist

Code

• Code is understandable and functions correctly
• Code is appropriately covered by automated testing

Pull Request

• Release notes are included if it's a change a customer could notice
• Testing section is appropriate and accurate

Security

• Does not check-in any secrets (e.g. passwords, api tokens)
• Does not log any sensitive data (e.g. customer pii, passwords). This includes FullStory!

All items above must be checked off before the PR may be merged.

[albertrdixon]

this entrypoint script handles the use case in which we must pass database client certificates as environment variables

[egtann]

LGTM!