first pass: create mock interface and classes for infrastructure API

[deepak-swirlds]

As part of this task develop a first draft of how the infrastructure API would look like.
It will take time for the infrastructure API to evolve, but this will serve as a draft for review comments by the team.

Deliverables:

• Mock Interfaces and Classes
• Class diagrams and sequence diagrams

### Tasks
- [ ] https://github.com/hashgraph/full-stack-testing/issues/382
- [ ] https://github.com/hashgraph/full-stack-testing/issues/447