Since Rails 5.0 the `protect_from_forgery` callback doesn't run first by
default anymore. [1]
Instead it gets inserted into callbacks chain where callbacks get
called in order.
This commit forces the callback to run first.
[1]: 3979403781
+ Use NullMetrics to mock metrics when unused
+ Use method_missing in NullMetrics mocking
+ Update prometheus gem to version that correctly uses transitive dependencies
+ Ensure correct folders are used in Multiprocess prometheus client tests.
+ rename Sessions controller's metric
