Improve node metrics

[jm-clius]

Minor PR towards #828

It adds:

1. A dimension to the message counter to keep track of the number of contentTopics in the network. This should enable us to build Prometheus queries to view i.a. the number of applications using the network.
2. A metric to track the number and type of connections initiated by the nwaku node. This will allow us to monitor number of connections initiated due to static configuration, dns discovery, discv5, API calls, and more.
3. Some error handling for failed connections initiated by this node.

For (2) it was necessary to clean up the connect and dial API in wakunode2 (somewhat).

There is some parallel work ongoing to update the bundled Grafana dashboard accordingly.

[status-im-auto]

Jenkins Builds

❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
✔️	8a576ed	#1	2022-01-25 16:16:31	~14 min	macos	📦bin
✔️	8a576ed	#1	2022-01-25 16:17:33	~15 min	linux	📦bin
✔️	8a576ed	#1	2022-01-25 16:34:46	~32 min	windows	📦exe
✔️	ae3e1cc	#2	2022-01-26 09:20:33	~11 min	linux	📦bin
✔️	ae3e1cc	#2	2022-01-26 09:21:03	~12 min	macos	📦bin
✔️	ae3e1cc	#2	2022-01-26 09:34:40	~25 min	windows	📦exe

[staheri14]

Looks good!