Add failongiterror as parameter to report any git error as NuKeeper e…

[MartinDemberger]

:sparkles: What kind of change does this PR introduce? (Bug fix, feature, docs update...)

A new option is added. When the option FailOnGitError is set the run failes when the call to get the available versions failes.

This is only the first part of a fix for #930

:arrow_heading_down: What is the current behavior?

On most of git calls the error is ignored and NuKeeper notifies success.

:new: What is the new behavior (if this is a feature change)?

A new option --failongiterror is introduced and when this option is set an error in a git call results in an error of NuKeeper.

In the current process the option is only used when searching for the available package versions.

:boom: Does this PR introduce a breaking change?

No, the default behaviour is unchanged.

:bug: Recommendations for testing

:memo: Links to relevant issues/docs

:thinking: Checklist before submitting

• [X] All projects build
• [X] Relevant documentation was updated

[stale[bot]]

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