major: add schema support

[moritzraho]

Description

This is a breaking change: validation + new export signature

• expose { load, validateAppConfig, coalesceAppConfig } vs previous load function
• Schema validation for app.config.yaml (taken & modified from https://github.com/adobe/aio-cli-plugin-app/blob/master/schema/app.config.yaml.schema.json)
• Coalesce configuration and $includes into one json before validation. Resolve path config values.
• Add schema for configSchema (top level config)
• Precise web cdn config.
• Add schema for events

Kept for later:

• Add action names/packages field limits
• Add events required fields, additionalProperties=false + limit/validations
• schema and typescript definition for the output object
• autocompletion with schema?

Related Issue

#11

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #21 (643de97) into master (ca93bf4) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 643de97 differs from pull request most recent head ba636bb. Consider uploading reports for the commit ba636bb to get more accurate results

@@            Coverage Diff            @@
##            master       #21   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            1         1           
  Lines          226       243   +17     
  Branches        65        69    +4     
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+ Hits           226       243   +17     

Impacted Files	Coverage Δ
src/index.js	100.00% <100.00%> (ø)

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[MichaelGoberling]

LGTM!

Q: Do we need to add the operations key that can be found in ext.config.yaml?

[moritzraho]

good point, done!

Could you give another review? I have moved configSchema to the top level and added a validation for events as well

[purplecabbage]

This should have had more discussion, I think this is a mistake to implement this here.