Bug 1693140 - Fix the mermaid rendering issue.r=ahal

sphinxcontrib-mermaid loads the mermaid library in different way which prevents mermaid library to load on production, it will work locally but not on writethedocs, so we have to hard loading the mermaid library through CDN in our tree.

Differential Revision: https://phabricator.services.mozilla.com/D111161

docs/conf.py

@@ -77,6 +77,7 @@ html_logo = os.path.join(
     topsrcdir, "browser/branding/nightly/content/firefox-wordmark.svg"
 )
 html_favicon = os.path.join(topsrcdir, "browser/branding/nightly/firefox.ico")
+html_js_files = ["https://cdnjs.cloudflare.com/ajax/libs/mermaid/8.9.1/mermaid.js"]
 
 exclude_patterns = ["_build", "_staging", "_venv"]
 pygments_style = "sphinx"