EZP-32017: fix trusted proxy setup for platform.sh

[ITernovtsii]

Question	Answer
JIRA issue	EZP-32017
Type	Bug
Target version	1.0
BC breaks	no
Doc needed	no

platform.sh use "ngx_http_realip_module" nginx module, and put client IP into REMOTE_ADDR. This makes it impossible to configure an application to be accessible from both with and without varnish.

If you'll put REMOTE_ADDR in TRUSTED_PROXIES, admin panel will be open to IP address spoof using "x-forwarded-for" header. And, the user will be able to request your varnish invalidation token.

If you'll put other IP addresses, or don't specify TRUSTED_PROXIES at all, you'll receive "Unauthorized" from varnish (because of "/_ez_http_invalidatetoken" route checking "$request->isFromTrustedProxy()", which will return false).

This PR makes it possible to have varnish without defined TRUSTED_PROXIES

Related to https://github.com/ezsystems/ezplatform/pull/609 but completely different)

TODO:

• [x] Implement feature / fix a bug.
• [x] Implement tests + specs and passing ($ composer test)
• [x] Fix new code according to Coding Standards ($ composer fix-cs).
• [x] Ask for Code Review.

[ITernovtsii]

let me know if it's not something you would like to release for 2.5 and I'll rebase to 3.2

[ITernovtsii]

So, the purpose of tokenAction() is no longer to actually return the invalidate-token, but to validate that a given token is correct. To make that clear to everybody, I think we should state that in PHP doc for this method.

I would like to keep the token returned to varnish. Varnish will cache it and don't bother PHP for PURGE requests with invalid token. But this will work only if the cache doesn't Vary by X-Invalidate-Token. I think it doesn't, but I'll recheck to be sure.

[ITernovtsii]

@vidarl I rechecked and see token validated properly (on varnish) for requests with invalid token, without sending /_ez_http_invalidatetoken to backend. So, I would vote to keep PR as is, without BC changes.