[HttpKernel] Make sure HttpCache is a trusted proxy

| Q             | A
| ------------- | ---
| Bug fix?      | yes (of sorts)
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9292
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/pull/4239

Fixes #9292 by adding `127.0.0.1` as a trusted proxy when using `HttpCache` (assuming it hasn't been already).