Add meta yaml schema

[cisaacstern]

Closes #93
Towards #84

To start, this is just a copy of the contents of https://github.com/pangeo-forge/meta-yaml-schema.

I will make adjustments before merging, namely:

• Don't require Pydantic dependency
• Provide minimal schema option which excludes provenance (and only has recipe object section)
• Update extended schema to reflect current provenance
• Provide optional validation of meta-yamls (maybe push to future PR, non-essential)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (005951c) 96.11% compared to head (089bcc2) 96.46%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #134      +/-   ##
==========================================
+ Coverage   96.11%   96.46%   +0.35%     
==========================================
  Files          14       15       +1     
  Lines         463      509      +46     
==========================================
+ Hits          445      491      +46     
  Misses         18       18              

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[cisaacstern]

Converting this to a draft as I am going to shift effort towards #137 as a first pass at this concept with a much lighter footprint. Leaving this open for further discussion at a later date.

[cisaacstern]

Turns out #137 is a nearly direct replacement for this, but in traitlets! So closing this!