Use the shared secret registration API directly (#7774)

* Use the shared secret registration API directly

rather than invoking the synapse module to do it. It's probably
a bit simpler, if anything, and allows for synapse to be run in
a separate container (or rather, avoids the javascript having to have
a copy of synapse source & server config).

* Make registration secret required

Update commander (8 major versions!) to get requiredOption

* Wrong options object :/

test/end-to-end-tests/package.json

@@ -11,7 +11,7 @@
     "license": "ISC",
     "dependencies": {
         "cheerio": "^1.0.0-rc.2",
-        "commander": "^2.19.0",
+        "commander": "^9",
         "puppeteer": "10.0.0",
         "request": "^2.88.0",
         "request-promise-native": "^1.0.7",