add typecode standard patters to schema

[mslarae13]

To develop a consistent and well defined schema, we should capture how to make a typecode and ensure it's easy for people to identify when to apply specific practices.

criteria for completion

• add slot standards to schema
• define the standards and when/how to use them. For example, sm= sample , actv = activity
• define when the parent class should be included in the subclass typecode (for example wf for workflow added to the typecode for "MetatranscriptomeAnnotationActivity" wfmtan)

[mslarae13]

relates to microbiomedata/nmdc-metadata#2