[BB-8933] Update template to support Redwood Release

Description

This MR updates the grove-template to support the Redwood release of Open edX.

Checklist

• Update edx-platform release branch references to redwood
• Update the default config (config.yml, grove.yml, requirements.txt)
• Update the config for example instance (config.yml, grove.yml, requirements.txt)

Dependencies

• Grove v0.18.x - v0.18.0-rc1
• tutor-contrib-grove 18.x - v18.0.0
• tutor-contrib-s3 - bump support for tutor 18