tl;dr: add "internal" as a valid audience designation, with functionality set "published".
====Details====
[] adjust [[ https://gerrit.wikimedia.org/g/mediawiki/core/+/1eeccc2d758e5c7e829fe6380954de5e9343f14f/tests/phpunit/structure/RestStructureTest.php#373 | the regexes in RestStructureTest::testModuleDefinitionFiles() ]]to allow "internal"
[] remove the TODO comments about allowing other suffixes (because now the multiple-suffix pattern will be established)
[] add "internal" to the mapping of audience designations to functionality sets (from {T422754}, following the pattern established under that task)
Note: "internal" eventually become "opt-in", but we won't yet have the ability to visually distinguish modules in the REST Sandbox. For now, "published" is the best we can do. Alternatively, this task could be deferred until visual distinction is possible, and "internal" could be mapped to "opt-in".