Add extra testing for nodes claims process #242

Specification

Currently, there only exists a success test (for both client-side and server-side) and a couple of exception tests (for the server-side, in GRPCClientAgent.test.ts). Ideally, this should be extended for all possible exceptions on the server-side, and any other potential problems that can arise during this process. (This was originally omitted due to time constraints - it's slightly tedious and time-consuming to write these larger scale tests.)

Furthermore, it would be worthwhile to further investigate the possibility of mocking the server-side such that we can introduce more granular testing of the client side process.

Additional context

• original thread regarding mocking the server (good overall information) https://gitlab.com/MatrixAI/Engineering/Polykey/js-polykey/-/merge_requests/209#note_673041297
• the original nodes claims MR https://gitlab.com/MatrixAI/Engineering/Polykey/js-polykey/-/merge_requests/209
• original nodes claims issue Creating a cryptolink claim from node to node (cross-signing claims) #213
• Apply timedCancellable to Sigchain such as the deadline in nodes claim process #243 - Adding in deadlines to the nodes claim process

Tasks

1. Create jest tests for each possible exception in the claims process. This can currently only be done for the server-side (by mocking the client) within GRPCClientAgent.test.ts
2. Investigate the possibility of mocking the server to produce granular testing for the client-side process (within NodeManager.test.ts/NodeConnection.test.ts)