Add missing API root for external logs requests

Somehow the external logs APIs in the client never used the API
root when constructing the URL. This means that if the Dashboard
is deployed at a non-root path, the requests never made it to
the logs proxy.

Update the external logs URL util to include the API root in the
same manner as we already do for all other APIs.

src/api/index.js

@@ -153,7 +153,7 @@ export function getExternalLogURL({
   if (queryString) {
     queryString = `?${queryString}`;
   }
-  return `${externalLogsURL}/${namespace}/${podName}/${container}${queryString}`;
+  return `${getAPIRoot({ isDashboardAPI: true })}${externalLogsURL}/${namespace}/${podName}/${container}${queryString}`;
 }
 
 export function getPodLogURL({ container, name, namespace, follow }) {