Reduce Dockerfile build time by referencing prebuilt image

[mrfelton]

This workflow currently rebuilds the Dockerfile from scratch on every run. This process takes over a minute to complete. We can significantly improve the build time (to just seconds) by referencing a prebuilt Dockerfile image.

Proposed solution:

Build the Docker image, push to your registry, and then reference that.

See actions/container-prebuilt-action (https://github.com/actions/container-prebuilt-action) for one way to do it.

Another way would be to use your prebuilt version as a base image for the Dockerfile in this repo. That would still incur some Dockerfile build time, but it would be a fraction of the time it takes to build the current Dockerfile. Would be more similar to what you do with your other action here https://github.com/launchdarkly/find-code-references/blob/main/Dockerfile

This will dramatically reduce the build time within workflows that leverage this action.

Benefits:

• Faster workflow execution times
• Improved efficiency