Autoconfigure service locator tag

[javiereguiluz]

symfony/symfony#26341

Probably it won't require any change in docs because we don't list the autoconfigured tags.

[codedmonkey]

I was just working on a PR related to this #9223. I tried to think of a nice way to incorporate it, but there doesn't seem to be a way without being reduntant about the default services.yaml configuration, and since it's completely optional I'd say it doesn't need to be documented.

[javiereguiluz]

At the end this was easier than I thought, so I'm trying to fix it in #9505.