Update Mockttp for key logs, webhooks, H2 fixes & HTTP streaming events

Lots of nice things included in here, amongst quite a bit of tidy up and
general improvement. Streaming events here particularly adds response
initiated and response & request body part events, opening up a whole
new API for the UI which should improve responsiveness, reduce
buffering, improve UX, and allow access to all kinds of awkward stream
requests & responses.

This also improves the admin stream handling of disconnection, opening
up a world where we handle that better/non-destructively, stops the
admin server processing events for subs nobody is using, and fixes lots
of minor event timing data bugs.

Lots to do to actually integrate & expose this, but watch this space.

Author: pimterry

package-lock.json

@@ -83,7 +83,7 @@
     "mime-types": "^2.1.27",
     "mobx": "^6.3.5",
     "mockrtc": "^0.5.0",
-    "mockttp": "^4.1.0",
+    "mockttp": "^4.2.0",
     "node-fetch": "^2.6.1",
     "node-forge": "^1.3.0",
     "node-gsettings-wrapper": "^0.5.0",