[hp-branch-rename] Implement hands-on T6L4/hp-branch-rename (#199)

# Exercise Review

## Exercise Discussion

Fixes #141 

## Checklist

- [ ] If you require a new remote repository on the `Git-Mastery`
organization, have you [created a
request](https://github.com/git-mastery/exercises/issues/new?template=request_exercise_repository.md)
for it?
- [ ] Have you written unit tests using
[`repo-smith`](https://github.com/git-mastery/repo-smith) to validate
the exercise grading scheme?
- [X] Have you tested the download script using `test-download.sh`?
- [X] Have you verified that this exercise does not already exist or is
not currently in review?
- [ ] Did you introduce a new grading mechanism that should belong to
[`git-autograder`](https://github.com/git-mastery/git-autograder)?
- [ ] Did you introduce a new dependency that should belong to
[`app`](https://github.com/git-mastery/app)?

Author: jovnc

hands_on/branch_rename.py

@@ -0,0 +1,46 @@
+import os
+
+from exercise_utils.file import create_or_update_file
+from exercise_utils.git import add, checkout, commit, init, merge_with_message
+
+__requires_git__ = True
+__requires_github__ = False
+
+
+def download(verbose: bool):
+    os.makedirs("samplerepo-books")
+    os.chdir("samplerepo-books")
+    init(verbose)
+
+    create_or_update_file(
+        "horror.txt",
+        """
+        Horror Stories
+        """
+    )
+    add(["."], verbose)
+    commit("Add horror.txt", verbose)
+    
+    checkout("textbooks", True, verbose)
+    create_or_update_file(
+        "textbooks.txt",
+        """
+        Textbooks
+        """
+    )
+    add(["."], verbose)
+    commit("Add textbooks.txt", verbose)
+
+    checkout("main", False, verbose)
+    checkout("fantasy", True, verbose)
+    create_or_update_file(
+        "fantasy.txt",
+        """
+        Fantasy Books
+        """
+    )
+    add(["."], verbose)
+    commit("Add fantasy.txt", verbose)
+
+    checkout("main", False, verbose)
+    merge_with_message("textbooks", False, "Merge branch textbooks", verbose)