Add more size intervals to obj size histogram

[krisis]

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Description

New intervals:
[1024B, 64KiB)
[64KiB, 256KiB)
[256KiB, 512KiB)
[512KiB, 1MiB)

The new intervals helps us see object size distribution with higher resolution for the interval [1024B, 1MiB).

Motivation and Context

To learn more about object size distribution between 1024B to 1MiB.

How to test this PR?

 mc stat myminio/bucket --json | jq '.Usage.objectsSizesHistogram'
 {
  "BETWEEN_1024B_AND_1_MB": 1,
  "BETWEEN_1024_B_AND_64_KB": 1,
  "BETWEEN_10_MB_AND_64_MB": 0,
  "BETWEEN_128_MB_AND_512_MB": 1,
  "BETWEEN_1_MB_AND_10_MB": 0,
  "BETWEEN_256_KB_AND_512_KB": 0,
  "BETWEEN_512_KB_AND_1_MB": 0,
  "BETWEEN_64_KB_AND_256_KB": 0,
  "BETWEEN_64_MB_AND_128_MB": 0,
  "GREATER_THAN_512_MB": 0,
  "LESS_THAN_1024_B": 1
}

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Optimization (provides speedup with no functional changes)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Fixes a regression (If yes, please add commit-id or PR # here)
• Unit tests added/updated
• Internal documentation updated
• Create a documentation update request here

[vadmeste]

Any reason why we are introducing a new version here ? the histogram is just a map. I am not able to see why the version change is required.

[krisis]

Any reason why we are introducing a new version here ? the histogram is just a map. I am not able to see why the version change is required.

sizeHistogram is a fixed-size array serialized as that in msgpack too. The histogram we see in prometheus is a map[string]int64 like you point out, but that's in the presentation layer.

[vadmeste]

LGTM