feat(contracts): add a availableExpectations field

[guzmud]

Backstory

Following the changes made to the injector contract with OpenAEV-Platform/openaev#5148 and OpenAEV-Platform/openaev#5554, the injectors are expected to send back two distinct lists availableExpectations ("@param availableExpectations the full list of selectable expectations") and predefinedExpectations ("@param predefinedExpectations the default expectations to include").

Current workaround

None.

Proposed solution

The ContractExpectations class must be updated with a new availableExpectations similar to predefinedExpectations in typing.

[guzmud]

Note for reviewers and bystanders: the issue regarding DRY has been taken into account, a follow-up issue have been written here #305