Use smaller per part size to use lower memory

[harshavardhana]

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

Verification

[bwplotka]

I think this is changing what was actually intended in the configuration as PartSize, let's figure out solution first on issue. Also ideally any of such changes will be benchmarked first, before applying 🤗

[bwplotka]

Performed some benchmarks and added benchmark to this PR 🤗

	// Uploading 100MB with:
	// PartSize: 1024 * 1024 * 100 = BenchmarkUpload-12    	      84	 416025119 ns/op	421129826 B/op	     946 allocs/op  (400MB allocated for single op)
	// ParSize:  1024 * 1024 * 25  = BenchmarkUpload-12    	     100	 273648888 ns/op	106639830 B/op	    1576 allocs/op (100MB overallocated).
	// PartSize: 1024 * 1024 * 8   = BenchmarkUpload-12    	      97	 254052232 ns/op	35392395 B/op	    3078 allocs/op (Still 33MB allocated [8x4])

As expected @harshavardhana, wonder how it was before this change against race? 🤔

EDIT:

I reverted the race fix locally on my branch and the result is:

// PartSize: 1024 * 1024 * 100 = BenchmarkUpload-12    	      88	 282906636 ns/op	 1671249 B/op	     907 allocs/op
// PartSize: 1024 * 1024 * 8 =BenchmarkUpload-12    	     100	 300660587 ns/op	 2195440 B/op	    3044 allocs/op

The difference is significant.

[bwplotka]

Thanks for help @harshavardhana 🤗

Closing this in favor of #3968