Deprecate the proxy-manager package

[javiereguiluz]

Fixes #17531.

I didn't find any other occurrence of proxy-manager. In Symfony 6.2 removed almost everything about it, so let's remove this last mention.

[OskarStark]

What about rewording the versionadded in 6.2 branch to:

"Since 6.2 laziness is supported out of the box without using any additional package."

Lets remove the explicit mention of the package name, so we can keep it this way until 7.0, plus we have a reference also in 6.2+ for people who remember you need to do sth in the past to have laziness.

[OskarStark]

Thanks Javier!