[Bug]: No way to set server_hostname when setting up OIDC with the UI

### Verified issue does not already exist?

- [x] I have searched and found no existing issue

### What happened?

I configured the DNS name `actual.example.com` after setting the app up initially using forwarded ports and the `localhost` DNS name.

While doing the initial setup with the `localhost` DNS name, I used the UI to configure OIDC.

This caused actual to save `"server_hostname":"http://localhost:5006"` in the OIDC settings in the database.

When I got my `actual.example.com` DNS name set up, actual continued trying to use `http://localhost:5006` as the redirect base URL.

I tried setting the `ACTUAL_OPENID_SERVER_HOSTNAME` variable to `actual.example.com`, but it didn't change the value in the database. (Maybe because I omitted `https://`?)

I ended up updating the value in the database manually, and it's now working.

### How can we reproduce the issue?

1. configure a fresh install of actual server using the DNS name "localhost".
2. Add OIDC settings via the UI, while still using localhost.
3. Connect with the DNS name that fits the redirect configured in OIDC provider. Logging in should give a redirect error.

### Where are you hosting Actual?

Docker

### What browsers are you seeing the problem on?

Firefox

### Operating System

Linux