feat: add t0123 & t0113 - gateway - json - cbor - symlinks

[laurentsenta]

Contributes to #26

Tasks:

• 123: test_dag_pb_conversion
  • Test structure
  • implement dag node getter
  • Implement the body checks
• 123: test_plain_codec
  • Test structure
  • Implement the fixture codec for json
• 123: Pathing, traversal over DAG-JSON and DAG-CBOR
• refactor the fixture into a more usable apis.

Notes

bytes equalities
the current test compares kubo and gateway outputs bytes to bytes, for example:

ipfs dag get --output-codec dag-$format $DIR_CID > expected
test_cmp expected my_gateway_output

For simple cases, we replace with a higher level comparator (JSON uses reflect.DeepEqual),
We stick to a bytes-to-bytes comparison with CBOR for now.

[laurentsenta]

Using shell check, this is what happens on error:

[galargh]

🏆

[laurentsenta]

@lidel a note here, we ignore a few tests: they compare two requests with each other.
Instead, we test each request.