Use source repository storage for forking process

What does this MR do and why?

Contributes to https://gitlab.com/gitlab-com/request-for-help/-/issues/2431

Problem

Currently, Rails provides the forked repository storage to Gitaly. For multi-node configurations, this can lead to situations where the source and forked projects are located on different nodes. This configuration is not supported by Gitaly.

Solution

Always use the source repository storage when forking the project.

References

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• https://gitlab.com/gitlab-com/request-for-help/-/issues/2431

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