Weaver needs to add some facilities to test the policies

[lquerel]

To properly and fully test our policies, we need deeper integration in Weaver instead of relying solely on OPA for the tests. The reasoning is as follows:

• The names of the policy packages are meaningful for Weaver (i.e. before_resolution, after_resolution, ...), unlike with OPA, so ideally, we need to check that as well.
• The Rego extensions that we are likely to introduce in Weaver over time will only be testable within Weaver.
• While not specific to Weaver, in addition to the tests, we could combine both tests and Rego code coverage to aid the policy review process (code coverage is supported by Regorus).