Prepare repository for running RuboCop after every push to Gerrit

Move Bundler and RuboCop configuration files to the repository root.

Also fixed inheritance of RuboCop configuration files: .rubocop.yml
inherits from .rubocop_todo.yml, not the other way around.

Bug: 69245
Change-Id: I99b82a1d773a26dccff4d08a23bb793e8530e86f
Merge "Prepare repository for running RuboCop after every push to Gerrit"