[to #42510875]use sphinx book theme

Link: https://code.alibaba-inc.com/Ali-MaaS/MaaS-lib/codereview/9042850

docs/source/conf.py

@@ -76,7 +76,7 @@ exclude_patterns = ['build', 'Thumbs.db', '.DS_Store']
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 #
-html_theme = 'sphinx_rtd_theme'
+html_theme = 'sphinx_book_theme'
 html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 html_theme_options = {}