Add new test suite for hooks / context merging

[toddbaert]

The current evaluation.feature suite does a good job covering the basic behavior concerning providers / evaluation API, but things like context merging precedence and hook behavior aren't really tested here.

We should create a new suite that tests some of the above.

[chrfwow]

Do you consider the tests introduced with open-feature/spec#290 to be covering the hook behaviour?