[API] - Use Core, Codecov_Auth, Reports and Legacy_Migrations Models From Shared

[adrian-codecov]

You can likely divide this into smaller steps, but mainly:

• Use the shared commit that uses these models
• Import all the model.py code from shared to api
• Update tests as necessary
• Ensure migrations are chosen from shared migrations -> see MIGRATIONS_MODULES
• Adjust any necessary code

Future Followup PRs include

• Replace the usage of plan service to use the service from shared
• Replace the usage of archiveservice service to use the service from shared
• Delete individual migrations for all of these apps
• Delete and replace all the files/tests that were moved in this PR - ... :O Port Some API Models to Shared shared#139