Fork using only a single branch or tag

[sad75]

Feature Description

Fork is an important operation in some development processes. It will be much more convenient if the resulting repository will contain only the useful references and not all the ones from the original repository.

As it is possible with github , it could be achieved by selecting a branch or a tag for the clone operation.

Screenshots

[dsseng]

Working on it right now

/assign @sh7dm

[dsseng]

Implemented support to fork arbitrary branch, since some projects are developed not on the default branch

[dsseng]

Extra idea: maybe we should support the same option for migrations? It's maybe even more useful in such case when people migrate (essentially fork a repo to their instance) for development purpose