[Misc][Doc] Add the latest stable release url (#826)

### What this PR does / why we need it?
 Add the latest stable release url

Signed-off-by: hfadzxy <starmoon_zhang@163.com>

docs/source/conf.py

@@ -23,7 +23,8 @@
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 #
-# import os
+import os
+
 # import sys
 # sys.path.insert(0, os.path.abspath('.'))
 
@@ -119,6 +120,16 @@ html_theme_options = {
 # so a file named "default.css" will overwrite the builtin "default.css".
 # html_static_path = ['_static']
 
+READTHEDOCS_VERSION_TYPE = os.environ.get('READTHEDOCS_VERSION_TYPE')
+if READTHEDOCS_VERSION_TYPE == "tag":
+    # remove the warning banner if the version is a tagged release
+    header_file = os.path.join(os.path.dirname(__file__),
+                               "_templates/sections/header.html")
+    # The file might be removed already if the build is triggered multiple times
+    # (readthedocs build both HTML and PDF versions separately)
+    if os.path.exists(header_file):
+        os.remove(header_file)
+
 
 def setup(app):
     pass