Stop using branches to reflect environments and use variable files instead.

Tasks

• Rename master > main
• Delete develop branch
• Update nro-generator to change any hardcoded reference for master
• Update deploy scripts to change any hardcoded reference for master
• Rename the release pipeline to production
• Add environment based composer file
• Write script to merge environment requirements to composer-local.json
• Rename planet4-base-fork to planet4-base
• Update documentation to reflect the changes