Context

The integration tests in internal/integration are perhaps better suited to live in the mongo package.

Definition of done

1. Migrate internal/integration/*_test.go files to the mongo package
2. Rename prose test from *_test.go to *_prose_test.go, if that has not already been done. Or determine another way to segregate prose tests in the flat file format in the mongo package
3. use package mongo_test for these migrated files
4. Move integration/mtest to internal/test and remove the integration directory