Allow HEAD mathod in file-server

[carragom]

Is your feature request related to a problem? Please describe.

When using the http file server from the CLI as documented with the following command:

deno run --allow-net --allow-read --allow-sys jsr:@std/http/file-server

The HEAD http method returns a 405 method not allowed.

Describe the solution you'd like

Implement the HEAD method in the file server.

Describe alternatives you've considered

This was discussed in Discord and looks like serveFile does support HEAD but serveDir does not. Apparently the discrepancy does not make much sense.