[DependencyInjection] Document proxifying interfaces for lazy services

[tucksaun]

Symfony 4.2 introduced the possibility of lazy load services using final classes by proxyfying specific interfaces (symfony/symfony#20656), but this has not been documented yet.

Targeting 4.4 because 4.4 is the oldest maintained branch, but should I target 4.2 as this was introduced in 4.2?

Fix #10295

[javiereguiluz]

Tugdual, you did right submitting this PR to 4.4 branch because we no longer merge in unmaintained branches.

Also, thanks a lot for a fantastic contribution documenting a nice feature that never got docs 👏

[tucksaun]

🙇

By the way, thank you @javiereguiluz for all those nice little tweaks that really make the documentation shines 🙏

[javiereguiluz]

While merging this into upper branches ... I reached 6.2, where we "removed" proxies in favor of "ghost objects". See https://github.com/symfony/symfony-docs/blob/6.2/service_container/lazy_services.rst

I kept your contribution about "Interface Proxifying" but I wonder if it applies to 6.2 and up because of the removal of proxies. Thanks.

[tucksaun]

TBH I only tried this feature on a Symfony 5.4 project.
But I just had a quick look at 6.2 and I see the option to define lazy as an interface name and some test cases or fixtures using the 'proxy' tag syntax.

If I get it correctly, the "proxy" vs "ghost object" is more a matter of implementation detail, which means it would more be a wording issue.
If you want I can have a deeper look about it and let you know.

[tucksaun]

@javiereguiluz I reviewed the wording in the 6.2 branch and as the rest of the document also uses proxy I think it works well enough as-is :)