Updates to MongoDB Connection and Kubernetes

[raclim]

Fixes #3096

Changes:

• Updates connection to MongoDB to use async/await syntax in server.js and previewServer.js. Other files that use this connection should also eventually be updated.
• Increases the number of replicas within kubernetes_app.yml to account for increased traffic.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

[release-com]

Release Environments

This Environment is provided by Release, learn more!
To see the status of the Environment click on Environment Status below.

• p5.js-web-editor
  • app-ted79fa.release.editor.p5js.org/
  • preview-ted79fa.release.editor.p5js.org/

🔧Environment Status : https://app.release.com/public/Processing%20Foundation/env-45cfe79555