input: Write a python function to convert the contents of a file to uppercase.
  assert convert_to_uppercase('lowercase.txt') == 'THIS IS A TEST FILE CONTENT'
  assert convert_to_uppercase('example.txt') == 'HELLO WORLD'
  assert convert_to_uppercase('sample.txt') == 'PYTHON IS GREAT'
output: def convert_to_uppercase(file_path):
      with open(file_path, 'r') as file:
          content = file.read()
      return content.upper()