Opt out of adding git as a build-package

[lengau]

What needs to get done

Allow the application to opt out of adding git as a build-package if craft.git exists.

Depends on #900

Why it needs to get done

For future bases we want to be able to exclude having git as a build package.

[syncronize-issues-to-jira]

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The internal ticket has been created: https://warthogs.atlassian.net/browse/CRAFT-3763.

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