Use buffered file read for checksum calculation

[pbusko]

Proposed Change

As an operator
I want the executor to use buffered read of the files from UploadAction when it calculates sha256 and md5 sums
So that the complete files are not loaded in RAM, potentially consuming too much resources on a cell

Acceptance criteria

Scenario: a buildpack cache grows to several Gb and it has to be uploaded with the UploadAction
Given the standard configuration
When the executor tries to calculate sha256 and md5 sums of the file
Then it only loads small chunks at a time, preventing excessive resource usage

Related links

• https://github.com/cloudfoundry/executor/blob/78ff519666b527dac7465515c43f3a058f278419/depot/uploader/uploader.go#L113
• Do not read entire file in memory for hash calculation executor#122