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/core-modules/client-config/client-config.resolver.ts

@@ -41,7 +41,7 @@ export class ClientConfigResolver {
       sentry: {
         environment: this.environmentService.get('SENTRY_ENVIRONMENT'),
         release: this.environmentService.get('SENTRY_RELEASE'),
-        dsn: this.environmentService.get('SENTRY_DSN_FRONT'),
+        dsn: this.environmentService.get('SENTRY_FRONT_DSN'),
       },
     };