Surface interaction mismatches to the test running the validation

[surpher]

🗣 Context

When setting up a Pact test and running it, lots of times the expected request does not match the request being triggered. When that happens, an informative message at the failing test should be surfaced up to the failing test.
At the moment it only fails with Server error 500 and debug area shows the expected and actual request which is difficult to filter through.

💬 Narrative

When a request does not match the expectation
I want the context and reason for failing to be surfaced to the
So that it's easier for developer to understand why the test failed

📝 Notes

Branch off of https://github.com/surpher/PactSwift/tree/feat/v2.0.0

As a guide surpher/PactSwift v1.x surfaces the issue like so:

✅ Acceptance Criteria

GIVEN a triggered request does not match the expected request defined in builder
WHEN PactSwift throws an error from libpact_ffi
THEN the line in the test is highlighted with XCTestFail and contains:

• Reason for failure (eg: "Actual request does not match expected interaction")
• Expected request (eg: POST /v1/endpointName)
• Actual request (eg: POST /v1/endpointNmae)