feat: Add integration description to replayed request ENV

[barthez]

Description

Using request customizer add integration description at X_PACT_DESCRIPTION to rack request env, similar to X_PACT_PROVIDER_STATES. Remove this env in last middleware before rack reversed proxy. That would be accessible in custom middleware added to verifier.

Additionally, support v3 provider states as a list with name and parameters.

Reason

I'm implementing pact testing setup for GQL Gateway which basically passes the pact verification to downstream services connected to the gateway. I need the description so I could create a contract for the downstream service.

[bethesque]

I'm so sorry - I've only just seen this PR. Is it still required?

[barthez]

Yes! it would be great to have it!

[YOU54F]

Hi thanks for this @barthez, looks really interesting! Popping this on my radar to take a look at