[Security Solution] [Bugfix] add redirect for old external alert route to new one on events page (#146896)

as per https://github.com/elastic/kibana/issues/140158, old external
alert route should either take user back to main entity page or to
external alerts.

## Summary
Take advantage of `onlyExternalAlerts` param to redirect users with old
urls to the new one for external alerts.

The gif below shows the old url before hitting enter- causing the page
to redirect to the events page with external alerts checked.
![Recording 2022-12-02 at 11 54
26](https://user-images.githubusercontent.com/28942857/205355379-d0b3a396-8cdf-48f2-966d-82ad3d133676.gif)

Co-authored-by: Kristof-Pierre Cummings <kristofpierre.cummings@elastic.co>

x-pack/plugins/security_solution/public/hosts/pages/index.tsx

@@ -39,6 +39,17 @@ export const HostsContainer = React.memo(() => (
     <Route path={`${HOSTS_PATH}/ml-hosts`}>
       <MlHostConditionalContainer />
     </Route>
+    <Route // Compatibility redirect for the old external alert path to events page with external alerts showing.
+      path={`${HOSTS_PATH}/externalAlerts`}
+      render={({ location: { search = '' } }) => (
+        <Redirect
+          to={{
+            pathname: `${HOSTS_PATH}/${HostsTableType.events}`,
+            search: `${search}&onlyExternalAlerts=true`,
+          }}
+        />
+      )}
+    />
     <Route path={getHostsTabPath()}>
       <Hosts />
     </Route>

x-pack/plugins/security_solution/public/users/pages/index.tsx

@@ -20,7 +20,17 @@ export const UsersContainer = React.memo(() => {
       <Route path={usersTabPath}>
         <Users />
       </Route>
-
+      <Route // Compatibility redirect for the old external alert path to events page with external alerts showing.
+        path={`${USERS_PATH}/externalAlerts`}
+        render={({ location: { search = '' } }) => (
+          <Redirect
+            to={{
+              pathname: `${USERS_PATH}/${UsersTableType.events}`,
+              search: `${search}&onlyExternalAlerts=true`,
+            }}
+          />
+        )}
+      />
       <Route
         path={usersDetailsTabPath}
         render={({