Add Scope implementation to metadata module

[iramiller]

Summary

Implement basic metadata structure for Scope

Problem Definition

• Review proto message for appropriate identifiers and structure, update as needed
• Implement ValidateBasic for Scope
• Add New[Object] functions for creating an instance of Scope
• Create test suite to cover basic validation logic
• Implement appropriate Stringer interface method, add test case
• Create associated keeper file for Scope.
  • Get/Set/Remove methods for object 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
  • 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