additionalTypDefs parsing errors are silently discarded

[EmrysMyrddin]

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Description

Mesh wrongly think additionalTypeDefs is a path on syntax error.

Mesh try to recognize if the string passed in the additionalTypeDefs is an entire document or a path to document.

For this, it just tries to parse it and assert that it's a path if it fails, silently discarding parsing errors.

This leads to not so easy debug experience when you made a syntax error in your schema extension.

While we should perhaps emphasising that using a separate file is recommended, we should also provide a correct error reporting for every way of using the tool.

Bug reproduction

Try to start mesh with following config:

sources:
  - name: Hello World
    handler:
      jsonSchema:
        operations:
          - type: Query
            field: greeting
            method: GET
            path: /
            responseSample: greeting.json
additionalTypeDefs: |
  extend Query {
    id = Int # This is a syntax error
  }

Expected behaviour

It should show the parsing error instead of a "file not found" kind of error.