added the possiblility to add custom varaibles

[Akilan1999]

Add custom variable to extend the use case of P2PRC . The code snippet below shows a sample implementation of the following PR.

// sample implementation 
import (
    "git.sr.ht/~akilan1999/p2p-rendering-computation/config"
)

// Main function 
func main(){
  // Sets the Env variable name to TEST
  config.SetEnvName("TEST")

 // Reads from the config file based on the path 
 // provided in the env variable TEST
 config.ConfigInit()
}