Add ContractSpecification implementation to the metadata module

[iramiller]

Summary

Implement basic metadata structure for GroupSpecification

Problem Definition

• Review proto message for appropriate identifiers and structure, update as needed. Change repeated ConsiderationSpec to be a repeated list of RecordSpecification identifiers. (this is a new type for the Address class)
• Implement ValidateBasic for object
• Add NewContractSpecification functions for creating an instance of ContractSpecification
• Create test suite to cover basic validation logic
• Implement appropriate Stringer interface method, add test case
• Create associated keeper file for ContractSpecification.
  • Get/Set/Remove methods for ContractSpecifications in state store (include events and instrumentation publishing). Ensure remove method fails if there are any existing references to object. Update any indexes that might be useful for rapidly querying/accessing data for queries. Example: all scopes with a given value_owner
  • Add a special Create method that takes a P8e ContractSpec and parses into ContractSpecification and RecordSpecifications. Split out: Add ability to convert p8e ContractSpec to new ContractSpecification and RecordSpecifications. #113
  • Stateful validation of object (pull existing, verify any updates are allowed, etc)
  • Implement iterator using KVStorePrefixIterator and appropriate prefix
• Wire up msg_server and query_server endpoints to new keeper methods.

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned

[iramiller]

See #58 for details on the Record Specification identifier.

[iramiller]

Moving out of assigned/todo as this is blocked pending merge/resolution of #56