[gh classroom clone --mirror] Clone repositories using mirror behavior to have all branches locally

Is your feature request related to a problem? Please describe.
When cloning student-repos repositories for archives purpose it is necessary to get all the branches locally so that the content on Github can be removed safely.
Similarly if the assignment tolerate or require to provide multiple branches then it would benefit of having all branches locally when cloning repositories instead of pulling them afterwards from remote repository.

Describe the solution you'd like
When using the existing gh classroom clone command the possibility to add --mirror option which would reflect the usage of git clone --mirror https://git-scm.com/docs/git-clone#Documentation/git-clone.txt-code--mirrorcode

Describe alternatives you've considered
Scripting outside of gh cli using git directly to clone the repositories.

Additional context

Given that the underlying gh cli support adding git flags on the command line for clone operation it could be resolved by exposing this feature in gh-classroom cli. This solution would also resolves https://github.com/github/gh-classroom/issues/15

https://cli.github.com/manual/gh_repo_clone

# Clone a repository with additional git clone flags
$ gh repo clone cli/cli -- --depth=1

Comienza con el comando existente gh classroom clone y compara su gestión de las opciones de clonación con el comportamiento documentado de gh repo clone ... -- --depth=1. Confirma que la opción solicitada --mirror produce el equivalente de git clone --mirror para los repositorios de estudiantes y conserva localmente todas las ramas.