v2.15.6

Added

• Added bucketed prometheus metrics head_block_relative_time_sum to help investigate latency and pipeline performance:
  • "app=firehose_output" and "app=substreams_output" that shows latency between outputing live blocks and their blocktime.
  • "app=relayer" for latency at relayer's input
• Substreams: Fixed underflow in 'FailedPrecondition desc = request needs to process a total of x blocks' error when running from 'substreams run' with a start-block in the future.
• Bump base64 library to use a much faster one in reader
• dstore: bumped google storage lib to v1.59.1 to fix a bug in their multi-range downloader, in case it affects us