Support getting git log since previous build

[RobiNino]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• All static analysis checks passed.
• This pull request is on the dev branch.
• I used gofmt for formatting the code before submitting the pull request.

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Exposes a new function GetPlainGitLogFromPreviousBuild to get git log since the VCS revision in the X previous build (0 being the latest, 1, 2 ...)

[lesnerd]

Thanks

[lesnerd]

Looks good