chore(backend): Added stage and prod deployment pipelines with fly

[rajdip-b]

Fixes #55

Feature list

• Added Dockerfile in backend to containerize the API of culero. Currently, the build size is 700 MB which we can optimize later on.
• Added fly.backend.toml that contains the details related to the API instances. primary_region = "bom" This line might need to be changed as per the regional preference!
• Added a 2 workflow files that will trigger when a push is made to develop and main.

Todos

• Need to make sure no one can push to develop or main, apart from maintainers
• Need to make develop a protected branch
• Need to add secrets to the repository
• Add CNAME entries in DNS registrar

@hsb1007