fix: add JSON schema validation for pipeline.yaml and jenkins-x.yml

[abayer]

Submitter checklist

• Change is code complete and matches issue description.
• Change is covered by existing or new tests.

Description

Also added jx step syntax:

• jx step syntax schema - generates JSON schema for either pipeline.yaml or jenkins-x.yml
• jx step syntax validate buildpacks - which validates against jenkins-x-kubernetes and jenkins-x-classic from the local clones.
• jx step syntax validate pipeline - validates jenkins-x.yml (or another context if specified)

Note that this depends on https://github.com/abayer/jsonschema, which
I'll try to get in a PR to the original (https://github.com/alecthomas/jsonschema).

Special notes for the reviewer(s)

/assign @dwnusbaum
/assign @rawlingsj
/assign @pmuir
/assign @ccojocar
/assign @warrenbailey
/assign @hferentschik
/hold

Which issue this PR fixes

fixes #3728

[abayer]

I still need to add tests for jx step buildpack validate, and I'm not sure if we actually want to use my fork (https://github.com/abayer/jsonschema) or wait til I can get a PR in to the original.

[abayer]

Oh, I also updated jenkins-x*.yml in this repo to be valid, and verified that all of our existing build packs are valid too.

[abayer]

...and ignore those first couple errors - I rebased before they could even kick off and they barfed as a result. =)

[rawlingsj]

/lgtm

[rawlingsj]

@abayer just noticed you'd put this PR on hold, I've lgtm so if you're happy for it to merge just cancel the hold.

[abayer]

@rawlingsj - thanks, but I still want to add more tests and get a consensus on whether we want to use my fork of https://github.com/alecthomas/jsonschema. Oh, and whether we should be doing some kind of release note due to existing jenkins-x.yml files with invalid content failing once this goes live...

[abayer]

/assign @jstrachan

fyi, this now has jx step syntax and subcommands for validation and schema generation. =)

[abayer]

aaaaand opened alecthomas/jsonschema#32 to get the changes we need upstream.

[abayer]

/test integration

[abayer]

Gonna take this off hold once either my PR upstream gets merged or we know it won't. =)

[abayer]

Ok, new PR to jsonschema up at alecthomas/jsonschema#36 - the first thing the original PR did (keep from panicking on unnamed fields) got fixed in someone else's PR that got merged before mine, so the new PR just adds the ability to ignore types. Hopefully it'll get merged in the next couple days, I can switch to using the real version rather than my fork here, and this can go off hold.

[abayer]

/hold cancel

The PR we needed is merged, so this is good to go!

[rawlingsj]

/lgtm

[jenkins-x-bot]

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