Injector: parameterize by type of operations to inject

Context

This MR is a first step towards moving the injector library outside of proto_alpha (which is itself a first step for moving part of the rollup node outside of proto_alpha).

It parameterizes the injector with the type of operations to inject, which means that any component that uses the injector can decide of its own operations and how they are translated for the protocol.

The next step it to make the injector use an appropriate injection/simulation function which can handle the (non-protocol) parameter operations.

Next MR: !7673 (merged).

Manually testing the MR

Refactoring only (excepted small change in how injector tracks operations with indexes).