Add a getUrl to remote content, that looks to see if the url matches a

pre-configured site, and redirects the call to that.  If nothing
matches, it falls back on 'default'.

@@ -21,6 +21,7 @@ export const configSlice = createSlice({
     }
   },
   selectors: {
+    getSites: (state) => Object.keys(state.sites).filter(site => site !== 'default'),
     getSiteBaseUrl: (state, name) => state.sites?.[ name ]?.baseUrl,
   },
 })
@@ -73,6 +74,18 @@ export const store = configureStore({
   ]),
 })
 
+export const getUrl = async(url: string) => {
+  const state = store.getState()
+  const sites = configSlice.selectors.getSites(state)
+  for (const site of sites) {
+    const baseUrl = configSlice.selectors.getSiteBaseUrl(state, site)
+    if (url.startsWith(baseUrl)) {
+      return getSitePage(site, url.substring(baseUrl.length + 1))
+    }
+  }
+  return getSitePage('default', url)
+}
+
 export const getSitePage = async (site: string, page: string) => {
   const result = await store.dispatch(sitePageSlice.endpoints.getPage.initiate({ site, page }))
   return result