schema change logic, execution models, and metrics updates

[MiConnell]

This PR bring enhancements to

• the schema_changes model:
  • major refactor to improve performance, reduce complexity, and fix incorrectly flagged duplicate adds/removes
  • metric additions and meta formatting updates
  • type changes now only flag if major type changes (int to string flagged vs varchar(10) to varchar(max) not)
• models related to execution:
  • sources are now included in dim_ and fact_ execution models and should now properly flow through to schema changes (source_added, source_removed, etc)
• metrics:
  • added meta metrics where needed for reporting purposes