Server: Handle HEAD requests to frontend bootstrap resources

[averymd]

1. What is not working as documented?

On build 221118-e58fee0fb, Photoprism returns 404s for HEAD requests to URLs that return 200s when GET requests are made. This began mid-October; I presumably upgraded to the Sept 1 release then. I use HEAD requests to monitor the uptime of the app.

2. How can we reproduce it?

Steps to reproduce the behavior:

1. Set up build 221118-e58fee0fb (Photoprism Plus) in docker; it doesn't matter if webdav is enabled
2. With the container running, use curl to make a GET request to the login page and see that a 200 is returned in the headers: curl -i -s http://127.0.0.1:2342/library/login
3. Run a HEAD request against the same URL and get a 404: curl -I -s http://127.0.0.1:2342/library/login

3. What behavior do you expect?

The HEAD request should return the same status code as its matching GET request, as it did previously.

4. What could be the cause of your problem?

I'm not familiar with Go, but it was updated in the Sept 2022 release.

5. Can you provide us with example files for testing, error logs, or screenshots?

N/A, but I can provide some docker-compose details if that would be helpful.

6. Which software versions do you use?

(a) PhotoPrism Architecture & Build Number: ARMv7 build 221118-e58fee0fb,

(b) Database Type & Version: MariaDB 10.8

(c) Operating System Types & Versions: Raspbian GNU/Linux 10 (buster)

7. On what kind of device is PhotoPrism installed?

(a) Device / Processor Type: Raspberry Pi 4

8. Do you use a Reverse Proxy, Firewall, VPN, or CDN?

I usually run nginx as a reverse proxy, but the curl commands bypass it, so it shouldn't be relevant.

[lastzero]

Use the GET /api/v1/status endpoint:

https://demo.photoprism.app/api/v1/status

[lastzero]

It's fundamentally because we don't do a redirect for unhandled URLs anymore. To solve this, we can add a head handler in addition to get. Thought the framework catches this.