Refactor ParamsBuilder

[chancharles92]

utils/params_builder.rs is actually making test debugging much harder as there are so many hardcoded values/logics inside. It's hard to directly debug other CAP API tests without figuring out the inner logic of ParamBuilder's implementations. We should try to refactor this helper struct at some point. @alxiong

[alxiong]

a mocking library to consider: mockall which might lead to cleaner design. (not sure yet, need investigation)