Add support for git-svn type working copy

[bigfroggit]

PR Description

I am not a software programmer, but only a ASIC designer, so I don't known GO language. But in my development environment, only SVN can be use now. I ready like git, and lazygit, so I want to use git-svn tool to handle my SVN working copy, so I can use lazygit. But for git-svn type working copy, pull/push operations are not same to git type working copy, and only should use git-svn rebase for pull operation. So I add some code to let lazygit to support git-svn type working copy. The modifications are generated by AI, but I also tried to make the code be logic right base on my comprehension on lazygit code. The main chages are:

1. Recognize the working copy type by contents in .git directory, and will show a info on startup.
2. Use rebase for pull operations.

If you like my modification, I would be very happy if you can merge to main branch.

Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• If a new UserConfig entry was added, make sure it can be hot-reloaded (see here)
• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc