Fix infinite redirect of UI init page

[haoming29]

As recently found out in the Denver cache deployment and NSDF S3 origin deployment, the web UI is trapped in an infinite redirect at the server start (not yet initialized with admin password). This PR is to fix this issue.

To test the fix, follow the instructions below:

• Remove your admin password file (backup first): rm /etc/pelican/server-web-passwd
• Build and run an origin ./pelican origin serve
• Go to the admin website at https://localhost:8444/
• You should be redirect to the initialization code page at /view/initialization/code/

[CannonLock]

LGTM! @haoming29 Note that this won't close #1184 as I also make the mistake of expecting the error response to take the form { error: "" } which is a mistake.

[haoming29]

LGTM! @haoming29 Note that this won't close #1184 as I also make the mistake of expecting the error response to take the form { error: "" } which is a mistake.

Sounds good. I'll remove the link to close #1184