more prometheus metrics

[brenzi]

closes #1459 (or what's relevant)

enclave sourced metrics

• rpc request + submitted TrustedCall metrics
• STF execution duration histogram
• STF execution numbers of success and failed calls histogram
• fix top-pool-size which was brittle and drifted in the past
• Runtime total issuance
• parentchains last processed block taken from parentchain pallet
• AURA execution stages remaining durations histograms per stage
• state size as in-mem Bytes with shard identifier bs58 as label

service sourced metrics

• enclave balance on all parentchains with parentchainId and account ss58 as labels
• shard vault balance with shielding-target and account ss58 as labels
• sidechain: number of connected peers
• sidechain: last finalized block as reported by Integritee Network
• MRENCLAVE bs58 of self as label
• VERSION as label

test locally, add --enable-metrics:

./integritee-service -u ws://172.17.0.1 --ws-external --enable-metrics -c run --skip-ra --dev &> worker.log
# other terminal
curl localhost:8787/metrics

should roughly result in this: https://gist.github.com/brenzi/2e44db310fce7cde642a4a2e94604067

[clangenb]

Some minor things, but looks very good to me in general.

[clangenb]

Wonderful, thanks for the fixes. Looks good to me.