support .efi and .iso extension in dispatch path

[amd-aliem]

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
Configuring Boot from URL with the sysconfig command in the Embedded UEFI Shell
As a result the path that dispatch advertised on http://<serverIP>: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://<serverIP>:8080/dispatch?foo.efi