fix: sentry init is using the wrong environment (#4940)

In the previous PR #4912 it seems that I forgot to pass the environment
on the backend.
Here is a quick fix!

I also added some "doc" in the the .env.example

packages/twenty-server/src/engine/integrations/environment/environment-variables.ts

@@ -235,7 +235,7 @@ export class EnvironmentVariables {
     (env) => env.EXCEPTION_HANDLER_DRIVER === ExceptionHandlerDriver.Sentry,
   )
   @IsString()
-  SENTRY_DSN_FRONT: string;
+  SENTRY_FRONT_DSN: string;
 
   @ValidateIf(
     (env) => env.EXCEPTION_HANDLER_DRIVER === ExceptionHandlerDriver.Sentry,

packages/twenty-server/src/engine/integrations/exception-handler/drivers/sentry.driver.ts

@@ -14,6 +14,7 @@ export class ExceptionHandlerSentryDriver
 {
   constructor(options: ExceptionHandlerSentryDriverFactoryOptions['options']) {
     Sentry.init({
+      environment: options.environment,
       release: options.release,
       dsn: options.dsn,
       integrations: [
@@ -25,7 +26,6 @@ export class ExceptionHandlerSentryDriver
       ],
       tracesSampleRate: 0.1,
       profilesSampleRate: 0.3,
-      environment: options.debug ? 'development' : 'production',
       debug: options.debug,
     });
   }