CLI: Improve `photoprism dl` to support additional flags

[lastzero]

NAME:
   photoprism download - Imports media from one or more URLs

USAGE:
   photoprism download [command options] [url]...

DESCRIPTION:
   Download and import media from one or more URLs.

   Usage examples:

   photoprism dl --cookies cookies.txt \
    --header 'Authorization: Bearer <token>' \
    --method file --remux auto -- \
    https://example.com/a.mp4 https://example.com/b.jpg

   photoprism dl -a 'Authorization: Bearer <token>' \
          -a 'Accept: application/json' -- URL

OPTIONS:
   --dest PATH, -d PATH                                       relative originals PATH in which new files should be imported
   --impersonate IDENTITY, -i IDENTITY                        impersonate browser IDENTITY (e.g. chrome, edge or safari; 'none' to disable) (default: "firefox")
   --method METHOD, -m METHOD                                 download METHOD when using external commands: pipe (stdio stream) or file (temporary files) (default: "pipe")
   --remux POLICY, -r POLICY                                  remux POLICY for videos when using --method file: auto (skip if MP4), always, or skip (default: "auto")
   --sort FORMAT, -s FORMAT                                   custom FORMAT sort expression, e.g. 'quality,res,fps,codec:avc:m4a,size,br,asr,proto,ext,hasaud,source,id'
   --cookies FILE, -c FILE                                    use Netscape-format cookies.txt FILE for HTTP authentication
   --header HEADER, -a HEADER [ --header HEADER, -a HEADER ]  add HTTP request HEADER in the form 'Name: Value' (repeatable)
   --help, -h                                                 show help