docs: fix & add new detailed steps on setting up DB

[cfnelson]

Recorded steps taken to setup staging/production DB in MongoDB Atlas as well as creating a new organisation with billing for the client.

Total setup time once logged in was about 5-10 mins based on your familiarity.

MongoDB Atlas has very simple UI/UX for getting setup, semaphore still takes me longer to just edit a setup 😂 .

FYI: Atlas provides an API which means we can programatically create an Organisation/clusters and users. We could write a script to automate this whole process. See here for their API docs.

Changes Made: 💃

• Added detail steps to creating a new Organisation for client projects/billing for MongoDB Atlas in the Guides.
• Added quick highlight steps for creating the Staging & Production Clusters & DB users.
• Misc other formatting & slight changes

Notes: 📓

• Could easily add images/screenshots/gif to demo how simply it is.
• I think maybe this file should be split out into its own sub sections.
• Current high-level structure is a quite confusing for me.

[ghost]

I've also grabbed this Atlas setup stuff into the unified doc I'm working on in a separate PR.

[cfnelson]

Can we add images or gifs to the guides? e.g ->