Define base and instrument specific metadata classes

[samaloney]

Describe the feature

• Propose base metadata classe/s similar to what's done in sunraster
  https://github.com/sunpy/sunraster/blob/main/sunraster/meta.py can use
  https://lc-radio-workshop.github.io/requirements/ as a base

Proposed solution

• Implement instrument specific subclasses to map from the metadata fits,cdf,dictionaries to the properties