saved searches: email configuration only picked up after hard reload

[mrnugget]

• Sourcegraph version: 3.4.0
• Platform information: Fresh Sourcegraph Docker instance, Google Chrome Version 74.0.3729.157

Steps to reproduce:

1. Setup a fresh Sourcegraph instance, add an external service, make sure repositories are cloned
2. Go to /search/searches, click Add new search
3. Type in type:diff foobar as a search query
4. Check the checkbox next to Email notifications
5. See warning: Warning: Sending emails is not currently configured on this Sourcegraph server. Use the email.smtp site configuration setting to enable sending emails.
6. Go to /site-admin/configuration, add an email configuration and save:

   "email.address": "noreply@sourcegraph.com",
   "email.smtp": {
       "authentication": "PLAIN",
       "host": "smtp.example.com",
       "password": "supersecretpassword",
       "port": 9999,
       "username": "email-username"
   },

7. Again go to /search/searches, click Add new search, use type:diff foobar as search query
8. Check the checkbox next to Email notifications
9. BUG: see the warning again that emails are not configured
10. Do a hard reload in Chrome (Cmd+Shift+R)
11. Again go to /search/searches, click Add new search, use type:diff foobar as search query
12. Check the checkbox next to Email notifications
13. See no warning

Expected behavior:

I don't need to do a reload after saving the configuration

Actual behavior:

The saved searches form is not picking up on the updated site config until I do a reload

[github-actions[bot]]

Heads up @alicjasuska @felixfbecker @umpox @valerybugakov @5h1ru @pdubroy - the "team/frontend-platform" label was applied to this issue.