Create new Drupal 9 compatible release and update project page with Drupal 9 info

Problem/Motivation

Per #3092581: Drupal 9 Release plan for Smart Trim, the dev branch is Drupal 9 compatible but there is no release yet and the project page does not reflect this.

Proposed resolution

1. Create a release (note that @markie said in Slack that there is a regression that needs to be fixed first)
2. Update the project page to note the Drupal 9 compatibility (see Twitter post for examples: https://twitter.com/DropIsMoving/status/1130868996771844096)

Remaining tasks

1. Fix regression (https://www.drupal.org/project/smart_trim/issues/3131842)
2. Create release
3. Update project page

User interface changes

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

N/A