k8s: Add GHA workflow to build and upload init containers to Docker Hub

[kford-newrelic]

Description

As part of the k8s agent operator work, each agent needs to create a GHA workflow in GitHub - newrelic/newrelic-agent-init-container-releases that builds and uploads init containers to Docker Hub whenever there is a new agent version released.

Note docker containers will also need to be generated for all previous agent versions that will still be supported as of the end of Q1 2024.

The Python agent team will create a GHA workflow first that does this and each agent can copy modify it for their own agent.

Acceptance Criteria

Creation of a new GHA workflow

NOTE:
Before containers are uploaded, they should be tested. #2573

[workato-integration]

https://new-relic.atlassian.net/browse/NR-260179