ENH: add optional per version url in version-switcher (#575)

Co-authored-by: Chris Holdgraf <choldgraf@gmail.com>

docs/user_guide/configuring.rst

@@ -378,14 +378,16 @@ Add a JSON file to define your switcher's versions
 
 First, write a JSON file stating which versions of your docs will be listed in
 the switcher's dropdown menu. That file should contain a list of entries that
-each have one or two fields:
+each can have the following fields:
 
 - ``version``: a version string. This will be inserted into
   ``switcher['url_template']`` to create the links to other docs versions, and
   also checked against ``switcher['version_match']`` to provide styling to the
   switcher.
 - ``name``: an optional name to display in the switcher dropdown instead of the
   version string (e.g., "latest", "stable", "dev", etc).
+- ``url``: an optional URL. If provided, it links the version to ``url``
+  instead of ``switcher['url_template']``.
 
 Here is an example JSON file:
 
@@ -400,8 +402,9 @@ Here is an example JSON file:
             "version": "2.0"
         },
         {
-            "version": "1.0"
-        },
+            "version": "1.0",
+            "url": "https://mysite.org/en/1.0/index.html"
+        }
     ]
 
 See the discussion of ``switcher['json_url']`` (below) for options of where to

src/pydata_sphinx_theme/theme/pydata_sphinx_theme/_templates/version-switcher.html

@@ -58,7 +58,9 @@
             node.textContent = `${entry.name}`;
             // get the base URL for that doc version, add the current page's
             // path to it, and set as `href`
-            entry.url = buildURL(entry);
+            if (!("url" in entry)) {
+                entry.url = buildURL(entry);
+            }
             node.setAttribute("href", `${entry.url}${currentFilePath}`);
             // on click, AJAX calls will check if the linked page exists before
             // trying to redirect, and if not, will redirect to the homepage