backend: Add support for deleting dirs in GitHub CreateBranch

[septum]

Description

• Added support to delete directories while creating a branch, retrying the delete operation if the error message states that the filePath provided is a directory.

Testing Performed

Manual

[septum]

maybe not needed, but are there plans to add unit tests later?

Yes, we'll encapsulate the logic of CreateBranch and CreateCommit in a later commit. That will be the piece we'll mock in the tests.