Add ProxyTestCase

Add documentation

Fix config and add docs

Fix undefined index

Fix config key name

Fix test

Fix fetching container
Improve base_url explanation

Rename to getHttpClient()

* Rename getClient() to getHttpClient()
* Make convenience methods protected
* Remove getProxyClient() method from ProxyTestCase
* Prefix base_url with "http://" so we can use it safely for the HTTP client
* Update docs

Improve type hints

Remove leading whitespace
Merge pull request #122 from FriendsOfSymfony/testcase

Add ProxyTestCase