/login page with "no authentication" in server config is a dead end, no way to get back to product list

[whisperity]

Describe the bug
If a server is started by default with no authentication enabled, the login page is still rendered, but there is no way to get out of it without manually editing the URL: no entry in the form gets you to log in, not even the superuser.

CodeChecker version
22cada3

To Reproduce
Steps to reproduce the behaviour:

1. CodeChecker server
2. Take note of the generated superuser info.
3. firefox http://localhost:8001/login (simulating access from a bookmark, or from browsing history)
4. Try logging in with the superuser info.
5. "Invalid credentials!" message.

To get back to the server, the URL must be manually edited.

Notably, the CodeChecker icon at the top appears to be clickable, when clicked, it does the ripple effect, but unlike most websites (e.g., GitHub), it does not lead back to the mainest of main pages.

Expected behaviour
The log in UI queries the API whether authentication is needed, and, if not, redirects automatically to the main page.

Desktop (please complete the following information)

• OS: Ubuntu 20.04.6
• Browser: Firefox
• Version: 118.0.2