fix S3 multipart operations to respect S3_MAX_PARTS_COUNT

[xavierleune]

Hi there,

I'm using a s3 provider with a limit of 1000 parts per upload, unfortunately the operations use the hardcoded limit for AWS (10000) instead of using the configValue S3_MAX_PARTS_COUNT.
This pull request should fix that behavior.

Thanks,

[Slach]

thanks for contribution, let's wait when CI jobs finish

[coveralls]

Pull Request Test Coverage Report for Build 20451139392

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 16 of 24 (66.67%) changed or added relevant lines in 3 files are covered.
• 285 unchanged lines in 11 files lost coverage.
• Overall coverage decreased (-1.7%) to 67.029%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/backup/backuper.go	0	1	0.0%
pkg/storage/s3.go	2	3	66.67%
pkg/backup/upload.go	14	20	70.0%

Files with Coverage Reduction	New Missed Lines	%
pkg/backup/restore.go	1	71.75%
cmd/clickhouse-backup/main.go	2	75.21%
pkg/backup/upload.go	2	70.2%
pkg/storage/object_disk/object_disk.go	5	66.3%
pkg/config/config.go	8	72.64%
pkg/server/server.go	9	58.54%
pkg/status/status.go	9	67.43%
pkg/backup/backuper.go	17	70.95%
pkg/storage/general.go	22	61.02%
pkg/storage/s3.go	23	47.39%

Totals
Change from base Build 20439655853:	-1.7%
Covered Lines:	10901
Relevant Lines:	16263

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💛 - Coveralls