Backend - Env Scattering Issue and Create a Setting File

[minhngo3818]

The environment variables should be placed in one place and then export to other files. However, some env variables like "host", and "port", database URL, and so on are hard-coded or imported directly from .env file. Some framework like .Net or Django has a setting file to assign all env variable and then abstractly use it in other files. This way will help our code base more maintainable.

Issues:

• May use index js to add all setting variables, or create a setting file
• Collect all environment variables scattered over the codebase, and place them in that file (mostly env)
• Replace env variables in the code base with the exported values from the setting file.