Add Statement Distribution V2/V3 Metrics

[Overkillus]

Statement Distribution has those metrics registered:

        statements_distributed: prometheus::Counter<prometheus::U64>,
	sent_requests: prometheus::Counter<prometheus::U64>,
	received_responses: prometheus::CounterVec<prometheus::U64>,
	active_leaves_update: prometheus::Histogram,
	share: prometheus::Histogram,
	network_bridge_update: prometheus::HistogramVec,
	statements_unexpected: prometheus::CounterVec<prometheus::U64>,
	created_message_size: prometheus::Gauge<prometheus::U64>,

After the switch to V2 the metrics were not properly updated and they are not used in V2/V3. Only active_leaves_update and share are being reported in the V2/V3 protocol. Other metrics are only reported when using the legacy V1.

TODOs:

• Mark with comments (or maybe there's a nicer way?) which metrics are used by which version (v1/2/3)
• Add new metrics tailored to v2 (preferably new metrics instead of subscribing to the old ones)
• And new metrics relevant to v3

Note:
PR #3444 Adds 2 more metrics not mentioned here relevant to v2 that tracks requests dropped due to peer limiting and the number of times we reach max parallel requests limit.

[AndreiEres]

I'm going to take this one because I may need more metrics for statemant-distribution benchmarks.