Add Guide for configuring Keystone in production

[stennie]

Currently the only production tip appears to be in the README:

Running KeystoneJS in Production

When you deploy your KeystoneJS app to production, be sure to set your ENV environment variable to production.

You can do this by setting NODE_ENV=production in your .env file, which gets handled by dotenv.

Setting your environment enables certain features (including template caching, simpler error reporting, and HTML minification) that are important in production but annoying in development.

[stennie]

Related:

• Deployment Checklist on the Keystone GitHub wiki.
• Express production best practices for performance & reliability: https://expressjs.com/en/advanced/best-practice-performance.html
• Express production best practices for security: http://expressjs.com/en/advanced/best-practice-security.html
• MongoDB production notes: https://docs.mongodb.com/manual/administration/production-notes/
• MongoDB Security Checklist: https://docs.mongodb.com/manual/administration/security-checklist/
• #3257: Caching mechanism with nginx in front
• Deploying a Keystone App to Heroku (gist)

[Rajivkumar1234]

How do we configure the mongo database setting when we deploy for example a keystone js app on a linux server?