vcs: add Jujutsu support

[daehyeok]

Support for detecting Jujutsu projects.

Jujutsu is a VCS which designed to working with multiple backend. Jujutsu is designed so that the underlying data and storage model is abstract. Today, it features two backends—one of them uses a Git repository for storage, while the other is a native storage backend1.

*It also planed to replace Mercurial as an internal monorepo client at Google. (See the slides)

Testing
Manually verified that projectile-project-info and projectile-find-file working properly.

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by checking the relevant checkboxes):

• The commits are consistent with our contribution guidelines
• You've added tests (if possible) to cover your change(s)
• All tests are passing (eldev test)
• The new code is not generating bytecode or M-x checkdoc warnings
• You've updated the changelog (if adding/changing user-visible functionality)
• You've updated the readme (if adding/changing user-visible functionality)

Thanks!