support .efi and .iso extension in dispatch path

## **Issue**

HPE system proliant Gen10+ (possibly others as well) only allows http boot with a URL that ends with `.efi` or `.iso` through these documented methods:
[Configuring Boot from URL with the System Utilities](https://support.hpe.com/hpesc/public/docDisplay?docId=a00112595en_us&page=s_http_pre-boot_sys_util.html)
[Configuring Boot from URL with the sysconfig command in the Embedded UEFI Shell](https://support.hpe.com/hpesc/public/docDisplay?docId=a00112595en_us&page=v34108138.html)
As a result the path that dispatch advertised on `http://:8080/dispatch` is not accepted.

## **Possible Solution**
Update dispatch to respond to `/dispatch.efi` or `/dispatch.iso`.

## **Workaround**
Add a bogus query parameter ending in .efi:
```
http://:8080/dispatch?foo.efi
```