feat: improve slack notifications with thread and templates

[lucasoares]

This pull request introduces a 0.0.3 version of the Slack integration workflow with two main templates (post-to-channel and send-message) for sending messages to Slack channels, along with their respective implementations and documentation.

Documentation Updates:

• Documented the post-to-channel template, including its inputs, outputs, and usage examples for various scenarios such as replying in threads, custom templates, and editing messages.
• Documented the send-message template, detailing its modes (simple, template, default-template), inputs, and usage examples for custom attachments and templates.

Implementation of post-to-channel Template (Python-based):

• Implemented slack.py including support for custom templates, thread replies, and message editing. Outputs include thread timestamps and channel IDs for subsequent workflow steps.
• Added requirements.txt to include the slack_sdk dependency.
• Updated the Dockerfile (too many vulnerabilities in the image).

Implementation of send-message Template (Node.js-based):

• Added support to send thread replies
• Updated the Dockerfile
  • stop using node 14 (too many vulnerabilities in the image).

    Node.js version 14 has reached end-of-life (EOL) status. Specifically, version 14.x reached its end-of-life on April 30, 2023

  • it was using npm but the lock was created using yarn, now it is correct
• Changed the slack webhook dependency to use official package (@slack/webhook instead of the slack-webhook package 9 years without updated).
• Updated eslint version to be compatible with other packages