Automates release note generation

[JBAhire]

Description

• Addresses Automate release notes generation for Hypertrace repos hypertrace#156
• Adds Gren bot (https://github.com/github-tools/github-release-notes#feed-gren-) to get create automatic release notes.
• Added this as a part of publish workflow in GitHub actions so it will automatically run every time we publish new release.
• Added .grenrc.js which formats the output of GREN bot according to our requirements.

Testing

These are updated release notes for latest release in this repo generated by Gren bot

Ref PR: hypertrace/pinot#61

Checklist:

• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules

Documentation

This utility uses labels for grouping PRs into categories so please use appropriate labels in upcoming PRs.

In order to have splendidly generated release notes, we recommend to follow these conventions:

• Start the subject line with a verb (e.g. Change header styles)
• Use the imperative mood in the subject line (e.g. Fix, not Fixed or Fixes header styles)
• Limit the subject line to about 50 characters
• Do not end the subject line with a period
• Separate subject from body with a blank line
• Wrap the body at 72 characters
• Use the body to explain what and why not how