Support UniFi Controller about ferretdb HOT 2 OPEN

Things are definitely moving along - I'm running Unifi 7.5 w/ Mongo 4.4. With Ferret 1.21.0, it works, but:

• There's a bunch of these errors during the mongorestore

  {
    "FlagBits": "[]",
    "Checksum": int64(0),
    "Sections": [
      {
        "Kind": 0,
        "Document": {
          "ok": 0.0,
          "errmsg": "Index option \"ns\" is unknown",
          "code": 2,
          "codeName": "BadValue",
        },
      },
    ],
  }
  

• It uses way, way too much CPU - this is just from browsing the Web UI and responding to /inform requests from the APs.
  

from ferretdb.

Hey. I run the Unifi Controller semi-successfully on FerretDB with SQLite.

It exhibits strange behaviour, some pages don't load on the web ui, at least not on the first try.
I believe #3792 is necessary as I get a bunch of "$group accumulator \"$first\" is not implemented yet" error messages.

Because I use it with sqlite, I needed to tweak the Mongo URI in system.properties of the unifi controller to drop the user/pass.
Other than that, it seems to function enough to provision APs, though not with much joy.

from ferretdb.