Add support for loading the config from "package.json"

[ionut-botizan]

Description

This PR enables loading the configuration from the package.json file. This is one of the default locations cosmiconfig normally looks into when searching for configurations and it is also already listed as supported in the graphql-config documentation.

Fixes #692

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Tests have been added to the test suite.

Test Environment:

• OS: Windows 10 Enterprise | OS Version: 20H2 | OS Build: 19042.985
• GraphQL Config Version: 3.2.0
• NodeJS: v14.16.1

Checklist:

• I have followed the CONTRIBUTING doc and the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• [N/A] I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests and linter rules pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Further comments

Some of the new tests fail because of another newly discovered issue in an upstream package: EndemolShineGroup/cosmiconfig-typescript-loader#134

[kamilkisiela]

Thank you <3