Announcing release 2.8.9 of Oppia

[Akshay Anand]

Hi all,

   The main changes in this release are increased coverage for frontend tests, more services migrated to Angular8, usage of Github Actions for CI and the addition of a new RTE element to show concept cards.

   Please welcome Arnesh Agrawal, Aung Hein Oo, Gabriel Fuentes, Prasanna Patil, Prayush Dawda, Shivansh Rakesh, Sudipta Gyan Prakash Pradhan, Aaron Zuspan, and Cathleen Huang for whom this release marks their first contribution to Oppia!

Thanks to Abhith Krishna, Akshay Anand, Ankita Saxena, Brian Rodriguez, James James, Kevin Lee, Kevin Thomas, Luis Ulloa, Mariana Zangrossi, Nishant Mittal, Nithesh N. Hariharan, Nitish Bansal, Prasanna Patil, Rishabh Rawat, Rohit Katlaa, Sagang Wee, Sandeep Dubey, Sean Lip, Tyler Ishikawa, Vojtěch Jelínek, Will Li, and Amey Kudari, our returning contributors who made this release possible.

Finally, I'd like to thank Anmol Shukla, Chris Skalnik, Kevin Thomas, Nithesh Hariharan, Rohit Katlaa, Rishabh and Vojtech for their help with pre-release testing, bug-fixing, and QA, as well as Chris Skalnik for leading the QA team for this release.

Thanks,
Akshay Anand