Made changed required by downstream nodejs projects

[thehenrytsai]

Made changes required to enable this SDK to be imported to spin up a nodejs DWN. Outlining journey that was taken in this PR:

1. Downstream TS nodejs project is not able to import this SDK: Fixed incorrect types value in package.json, missing esm in path; but:
2. Crash on start because JSON-schema file import need import assertion: Fixed by adding import assertions; but:
3. Build failure upon adding import assertions: Fixed by update module value in tsconfig to enable import assertion syntax in TS. but:
4. ts-mocha throws TypeError: Unknown file extension ".ts" error when attempting to run tests using npm run test:ndoe: After trying many things with no success, decided to use this opportunity to ditch ts-mocha and ts-node entirely by using building the tests and run tests using mocha directly, this will give us true code coverage also; but
5. mocha fails importing files because esm requires explicit .js file imports but we don't do that: Added --es-module-specifier-resolution=node flag to make node import files correctly. but:
6. nyc code coverage tool also mysteriously stopped reporting code coverage at all: After trying many things with no success again, decided to replace nyc with c8, which is now a far more active code coverage tool than the stalled nyc anyways; but
7. Spinning up DWN require explicit construction of DID resolver which is a pain: Made it an optional parameter with ION being the default resolvable method.
8. Now the external DWN can finally officially run on nodejs for the first time, but immediately throws error for any request because the request parser does not JSON parse if input is an object, but raw input is actually ingested as an array of bytes, which is of object type: Refactored the code to parse the raw bytes before passing to request parser.