Feat: Reading usns from filepath

[pacostas]

Summary

This PR:

• Adds functionality for reading usns from a filepath. This is useful in case we want mulitple actions to read the same input. That way we avoid hitting the API multiple times.
• Changes the default number of pages that the action fetches from the API, from 2 to 1. This ends up with one request less to the API.
• Adds an extra argument called pages, in case someone would like to increase the number of pages, that the action fetches from the API
• Alters the Docker image, and instead of pre-building it and pushing it to a registry, it changes it in order to be consumed as a docker file as we do with the rest of the github actions.

Use Cases

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).