Tree: add "go up" the tree button

Created by: oleggromov

Description

Part of the Tree improvements, it adds the option to navigate up the tree.

The tree still retains the "confusing behaviour", which is the inconsistency between:

1. Navigating to the root of the repo - which opens up the entire tree at root, as expected
2. Going to a deeply nested file, which only opens the subtree - which is confusing

This part will be fixed later on, with a bigger refactoring of the entire Tree component, including data fetching, tree processing, and rendering.

Test plan

1. Check out the branch
2. Open up a few repos:
   1. A regular one with lots of subfolders: https://sourcegraph.test:3443/github.com/sourcegraph/code-intel-extensions
   2. Something with a deeply nested single children: https://sourcegraph.test:3443/github.com/sgtest/java-pom-with-deps-javaconfig/-/blob/src/main/java/com/sourcegraph/depuser/ApacheCommonsUser.java
   3. A single-file one: https://sourcegraph.test:3443/github.com/sgtest/head-branch/-/blob/foo
3. Make sure that ".." is shown and navigates up the tree
4. Make sure that tests are passing

https://user-images.githubusercontent.com/2196347/180196529-e712b6cb-2fef-4185-8079-2b12a328b4fb.mov

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.