Add ability to run hamilton-ui on domain subpath (#1284)

* feat: add support for custom sub-path in BrowserRouter

* chore: add documentation for ui subpath configuration

* docs: clarify subpath environment variable requirement

Author: jonas-meyer

docs/hamilton-ui/ui.rst

@@ -118,6 +118,14 @@ Self-Hosting
 If you know docker, you should be good to go. The one environment variable to know is `HAMILTON_ALLOWED_HOSTS`, which you can set to `*` to allow all hosts, or
 a comma separated list of hosts you want to allow.
 
+To host the UI on a subpath, set `REACT_APP_HAMILTON_SUB_PATH` to the subpath required. For example, to run on `https://domain.com/hamilton`:
+
+.. code-block:: yaml
+
+    - REACT_APP_HAMILTON_SUB_PATH=/hamilton
+
+Make sure that the sub path environment variable begins with `/` if set.
+
 Please reach out to us if you want to deploy on your own infrastructure and need help - `join slack <https://join.slack.com/t/hamilton-opensource/shared_invite/zt-2niepkra8-DGKGf_tTYhXuJWBTXtIs4g>`_.
 More extensive self-hosting documentation is in the works, e.g. Snowflake, Databricks, AWS, GCP, Azure, etc.; we'd love a helm
 chart contribution!

ui/frontend/src/App.tsx

@@ -28,6 +28,7 @@ import { UserContext } from "./auth/Login";
 import { LocalAccount } from "./auth/LocalAccount";
 
 export const localMode = process.env.REACT_APP_AUTH_MODE === "local";
+export const subPath = process.env.REACT_APP_HAMILTON_SUB_PATH || ""
 
 const useAuthInfoBasedOnProcEnv = () => {
   if (localMode) {
@@ -99,7 +100,7 @@ export const App = () => {
           includeHelp: true,
         }}
       >
-        <BrowserRouter>
+        <BrowserRouter basename={subPath}>
           <Routes>
             {localMode && (
               <Route path="/" element={<Navigate to="/dashboard/account" />} />