Move `mock-observations` to `if/builtins`

[zanete]

Sub of: #656

What Move the MockObservations plugin from if-plugins to if/builtins

Why This is part of our migration of our core plugins into a standard library in if/builtins.

Context This is a core feature we want to support, so it is migrating into if.

Prerequisites/resources no

SoW (scope of work)

• [ ] move plugin code into builtins/mock-observations
• [ ] fix any integration issues caused by the migration
• [ ] migrate and fix unit tests
• [ ] update README documentation updated

Acceptance criteria

• [ ] plugin code is migrated to if-builtins Given (Setup): The migration has been completed. When (Action): A user or developer navigates to if Then (Assertion): they will find a folder if/builtins/mock-observations containing the plugin source code and a README.

• [ ] plugin code and unit tests pass and maintain 100% coverage Given (Setup): The migration has been completed and a user has downloaded if. When (Action): they run npx jest --coverage Then (Assertion): they will receive a report showing 100% coverage and 100% passing

[zanete]

@manushak please review the PR

[manushak]

@manushak please review the PR

done