fix(modules/unifi): proper monitoring and latest version

They've recently removed from nixpkgs the version of mongodb that was
used by unifi. I updated to the latest version (7) and did the migration
of the DB manually (see https://github.com/NixOS/nixpkgs/pull/207382):

```
nix-shell -p mongodb-3_4 mongodb-tools
mongod --dbpath /var/lib/unifi/data/db  --logpath /var/log/unifi/repair.log --repair
mongod --dbpath /var/lib/unifi/data/db  --logpath /var/log/unifi/repair.log --journal --fork
mongodump --out=/root/mongodump
pkill mongod
exit
nix-shell -p mongodb-4_2 mongodb-tools
mv /var/lib/unifi/data/db /var/lib/unifi/data/db_bak
mkdir /var/lib/unifi/data/db
mongod --dbpath /var/lib/unifi/data/db  --logpath /var/log/unifi/repair.log --journal --fork
mongorestore /root/mongodump
pkill mongod
```

Once this was done, the exporter was also broken, has it has been
renamed. There are two different services for it in nixpkgs:
`services.unpoller` and `services.prometheus.exporters.unpoller`. Only
the last one works.

From what I can tell, everything is working now.

1 files changed, 4 insertions, 1 deletions

diff --git a/hosts/tahoe/secrets/secrets.nix b/hosts/tahoe/secrets/secrets.nix
index 38bb1b0..2d23fda 100644
--- a/hosts/tahoe/secrets/secrets.nix
+++ b/hosts/tahoe/secrets/secrets.nix
@@ -29,7 +29,10 @@ in
     owner = "fcuny";
   };
 
-  "unifi/unifi-poller.age".publicKeys = all;
+  "unifi/unifi-poller.age" = {
+    publicKeys = all;
+    owner = "unpoller-exporter";
+  };
 
   "restic/repo-systems.age".publicKeys = all;
   "rclone/config.ini.age".publicKeys = all;