input: Write a python function to convert HTML content to plain text.
  assert html_to_text("<p>Hello world!</p><div><p>This is a test.</p></div>") == "Hello world! This is a test."
  assert html_to_text("<h1>Title</h1><p>Paragraph</p>") == "Title Paragraph"
  assert html_to_text("<div><p>First</p><p>Second</p></div>") == "First Second"
output: def html_to_text(html):
      from bs4 import BeautifulSoup
  
      soup = BeautifulSoup(html, "html.parser")
      return ' '.join(soup.stripped_strings)