Update container push workflow to GHCR

[jhujasonw]

Apparently, the way to push containers to GH has changed and the example the current workflow is based on will no longer be valid soon. Better to switch over while we can and start fresh the "Right Way"

{
  "use": "issues2jira",
  "data": {
    "url": "https://jhulibraries.atlassian.net/browse/OPS-1586",
    "key": "OPS-1586"
  }
}

[jhujasonw]

This currently works with the merged PR, but there will be an update when GHCR comes out of beta and goes GA to hopefully use the GITHUB_TOKEN authentication method in the workflow. Leaving this issue open for that change when it comes.