Freecodecamp: Rename Master branch to Main and modernize references to master-slave db replication

[QuincyLarson]

We are changing freeCodeCamp's Master branch to "Main".

We are also going through our curriculum and our publication and changing references to Master-Slave Database Replication to "Primary" and "Replica".

Master was the default branch name on GitHub when we created this repo back in 2014, and GitHub itself is changing this going forward.

The terms "Primary" and "Replica" are clearer anyway, and we can avoid the baggage of this poorly-chosen naming convention from decades past.

Tasks:

• [x] All freecodecamp.org/news references to master-slave database replication and master branches are updated
• [ ] All freeCodeCamp GitHub repository branch names renamed
• [ ] Readme.md, Contributing.md, and other Documentation files on repos are updated

[raisedadead]

IMHO, instead of main we could do one better called it dev or development (I prefer later), which fits better in our context of other branches which we have been using for a while now:

master development
production-staging
production-current

Signifying the development process:

development --> production-staging --> production-current

[nhcarrigan]

Hello~!

If help is welcome, I'd be willing to update the documentation to reflect the name change. 🙂

[ieahleen]

I will follow this issue, so that I can update the italian docs when the change is done, and start working on them to make them a bit better and updated