[CJS-8565] local/dev mode

[jlombana-opti]

Summary

• the better way to work in local/dev is knowing in what environment we are. in cloudflare there is not a way to know that automatically. so the customer must set it up in the wrangler.toml.
• adding the host variable it means that is running in development mode.
• costumers are able to create variables per environment adding [env.<environment>.vars]. this variables don't inherits from other environments. thats why the customer have to define the variables on each environment.
• to run the starter with the environment variables. the customer have to add a command in the package.json with the environment flag --env=<environment>.
• to reduce mistakes in the url. added host, upstream_protocol, upstream_port, upstream_pathname variables. and we create the url.

Jira

• CJS-8565