Get UTxO-HD ready for handover

[dnadales]

We aim at producing a UTxO-HD enabled node that meets the performance requirements of all the stakeholders, and that passes the system-level tests. Successfully achieving this means we will have a version ready to be tested on a production environment (testnet and mainnet).

The UTxO-HD feature should be ready for production testing, which means:

• Bring query utxo by address command performance on par with current version #205
• Fix UTxO-HD issues found during B&T  #314
• Update the tracers to account for the new UTxO-HD code #227
• Implement legacy mode for UTxO-HD to keep baseline performance #429
• Prototype LedgerDB/BackingStore redesign to accommodate LSM-tree backend #510
• Switch over to the new LedgerDB API #815
• Implement LedgerDB V2
• Get sign off by system level benchmarks #203
• Get sign off by node integration tests #188
• The prototype implementation will be handed over for testing on testnet (by signalling readiness to @disassembler).
• Notify the following downstream clients about the upcoming release:
  • Mithril
  • Wallet
  • Db-sync

Note that merging the UTxO-HD feature branch into main depends on whether this blocks other workstreams.

Risks

• System level benchmarks might show regressions we have to eliminate.
• Integration tests might find errors we have to fix.

[jasagredo]

Node 8.2.1 (Being tested):

• UTxO-HD for node 8.2.1-pre cardano-node#5444
• UTxO-HD for node 8.2.1-pre cardano-api#203
• UTxO-HD for node 8.2.1-pre #315

Node 8.3.1 (we are going to omit this version, no longer updated):

• UTxO-HD for node 8.3 #320
• UTxO-HD for node 8.3 cardano-api#236
• UTxO-HD for node 8.3 cardano-node#5465

Node 8.4.0:

• UTxO-HD for node 8.4.0 #353
• UTxO-HD for node 8.4.0 cardano-api#251
• UTxO-HD for node 8.4.0 cardano-node#5476

Node 8.5.0:

• UTxO-HD for node 8.5.0 #412

Running issue: #314

[jasagredo]

UTXO-HD is ready for handover except if Benchmarks shows otherwise. Closing for now, will open a different issue with results if needed.