spike: consumer driven contract testing via Pact

[boonious]

Hui depends heavily on mock HTTP servers in testing. It also uses prebaked responses to a wide range Solr API requests. Pact contract testing can be replied upon to ensure that the test mocks are faithful and resilient to future Solr API changes.

Tasks

• spike/investigate ways of generating Pact contracts in Bypass expectations
• (if) submit PR for Bypass DSL to have options in Pact contracts generation
• implement Pact (Solr) provider verification via mix task and Docker instances
• update all unit/integration tests