metrics: Measure incoming block delays

[shohamc1]

Adds the following metrics via diagnostics API:

• Delay between header timestamp and header download
• Delay between header timestamp and body download
• Delay between header timestamp and block execution start
• Delay between header timestamp and block execution end
• Delay between header timestamp and starting to produce next start

The API returns up to 200 entries along with the minimum, maximum and average of the data set in the following format

{
    "max": 811023000,
    "min": 95364000,
    "average": 220728375,
    "data": [
        178573000,
        162932000,
        ...
    ]
}

[AskAlexSharov]

@shohamc1 please also add metric into turbo/execution/eth1/inserters.go:InsertBlocks - it's used instead of stage_bodies if --internalcl is set.