Wallet Metric

[peterjan]

This PR adds a WalletMetric so we can easily fetch the evolution of the balance over time. This would prevent the wallet page from having to load all transactions (80mb) to accomplish the same. This would allow @alexfreska to fetch the latest transactions (using limit=100) and create the balance graph using the metrics endpoint. This is consistent with hostd

	WalletMetric struct {
		Timestamp time.Time `json:"timestamp"`

		Address types.Address `json:"address"`

		Confirmed   types.Currency `json:"confirmed"`
		Spendable   types.Currency `json:"spendable"`
		Unconfirmed types.Currency `json:"unconfirmed"`
	}

[ChrisSchinnerl]

I think the address isn't very useful considering it never changes and is not something that you can visualise in a meaningful way.

[peterjan]

I was on the fence when I wrote it. I figured it couldn't hurt but removed it. It wasn't about ever needing to visualise multiple wallets or handle multiple addresses, it was more to ensure we never visualise anything we know not be related to "our wallet".

[peterjan]

kept this for consistency and extensibility

[ChrisSchinnerl]

lgtm but could still use an integration test to verify that we register metrics

[peterjan]

lgtm but could still use an integration test to verify that we register metrics

I actually added it and then removed it, I also tested it manually on my node. I'll add an integration test in a F/U PR.