Create a core config package which will have all the constants

[MehulKChaudhari]

Issue Description

Create a core config package move all const to this config package, then consume the configs

instead of this

feature-flag-backend/jwt/jwt.go

Line 40 in d640dca

SessionCookieName: os.Getenv("SESSION_COOKIE_NAME"),

We have to do something like this.
example:
https://github.com/Real-Dev-Squad/tiny-site-backend/blob/develop/config/core-config.go
https://github.com/Real-Dev-Squad/wisee-backend/blob/develop/src/config/core-config.go