Add a note that Symfony's recipe enables bundle for `prod`.

[MarcinOrlowski]

Problem Statement

Official integration docs for Symfony: https://docs.sentry.io/platforms/php/guides/symfony/ shows steps to follow to record first test error. But it lacks vital information, that when Symfony package is installed its recipe configures the bundle to be available in prod environment only. There's high chance that one will try to test it locally first before deployment and because s/he is usually on dev environment in that case, nothing will be really recorded giving false impression something is not working. Adding a note about that nuance would most likely be useful for new users (and yes, I stepped on this).

Solution Brainstorm

Update the docs.

[stayallive]

Maybe we should instead update the recipe to not have this prod filter?

Having the package installed but the DSN not provided should be enough to disable it sufficiently for local development. But I must admit I might be wrong here since I assume there is a reason the recipe was setup like that.

[Jean85]

IIRC Symfony maintainers suggested to config it for prod only, because the bundle inserts its own error handler, that may play badly with Symfony's or PHPUnit's; see the outstanding #337. I'm personally against this; I cannot find the issue where we discussed this though.

Right now, thanks to PHPUnit 10, this may no longer be an issue, so maybe we can push for revert this decision.

[stayallive]

Ah right, I can remember some discussions about that. Isn't there some way we can modify the integration to not register itself or the error handlers based on if the DSN is present at startup? I think there were some issues with that too but that might also solve the problem and remove the discussion.

[MarcinOrlowski]

Why simply not updating the documentation? That's all is needed to cover this case. No code change is required. Just document the current behavior and you are all good :)