CSFeeOracle based on BaseOracle and HashConsensus

[madlabman]

Lido v2 introduced several new contracts for oracles, including HashConsensus and BaseOracle. To make use of that, the set of contracts copied in the source tree under lib/base-oracle directory. OpenZeppelin contracts of version 4.4.1 added separately to resolve dependencies of the copied contracts (see remappings.txt). Only change for lido-dao contracts made is changing compiler version from 0.8.9 to ^0.8.9 to be able to seamlessly import the contracts.

The flow for the off-chain part may look like this:

• It queries the new frame like this:

        startSlot = consensus.getLastProcessingRefSlot();
        (refSlot, ) = consensus.getCurrentFrame();

• It queries oracle.treeCid and downloads previous report data if any.
• If no tree available, rebuild one starting from getFrameConfig.initialEpoch by traversing frames one by one.
• It sends the report.