Issue #2711099 by heddn, Jo Fitzgerald, edysmp, edgewl2, alexpott, Charlotte17, mikeryan, masipila, quietone, maxocub, phenaproxima: Categorize migrations according to their type

Issue #2917883 by quietone, TR, Jo Fitzgerald, masipila, phenaproxima: Rename 'migration_templates' directories in core modules to 'migrations'

Issue #2569805 by quietone, Jo Fitzgerald, mikeryan, joelpittet, heddn, Adita, Miguel.kode, iMiksu, tvb, maxocub, juancasantito, phenaproxima, alexpott, neclimdul, xjm: For Drupal migration, identify the source module