Added support for caching REST api calls to POST /api/ezp/v2/views

[vidarl]

Question	Answer
JIRA issue	N/A
Type	Feature
Target version	2.0
BC breaks	no
Doc needed	no

This is a change to the varnish .vcl that makes it possible to cache POST requests to /api/ezp/v2/views (which is basically a search ).
The /api/ezp/v2/views endpoint do not provide xkey header in the response so purging won't work, thus the TTL is set to 600 by default.

Don't think we should merge this as-is ( /api/ezp/v2/views should defently provide xkey headers first ). But posting the code here for reference. It might be valuable to others too.

Credits to @reithor and @adriendupuis who also worked on this code

TODO:

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