Unify env loading for apps

[ygrishajev]

This commit introduces a certain env loading logic into an application which is described in apps/api/README.md#environment-variables.

We need to spread the same approach to other applications.

• Create a new package env-loader which should basically expose the logic in this file as a function or a class method
• Update api to use the package

Update every app to use the package and create all the required env files with proper values, update .dockerignore and gitignore, make sure sample file is filled with all used vars. Use api commit as reference.

• deploy-web
• indexer
• provider-console
• provider-proxy
• stats-web

Required env files:
apps/api/env/.env
apps/api/env/.env.production
apps/api/env/.env.staging
apps/api/env/.env.mainnet
apps/api/env/.env.sandbox
apps/api/env/.env.sample

[baktun14]

I think this might be a duplicate of this one #163

[ygrishajev]

They overlap quite a bit but contain some differences. I'd leave this task as it's very specific and update the other one