make cli binary path configurable

Somehow on the server there's an issue with  (a) the snap binary that
can't load the config file and (b) the binary not being found in
`~/bin/` with just `should-i-watch-this`. Configuring the absolute path
to the binary works.

Author: koffeinfrei

www/app/models/movie.rb

@@ -1,5 +1,6 @@
 module Movie
   KEY_PREFIX = "siwt_movie"
+  CLI_BIN = ENV.fetch("CLI_BIN", "should-i-watch-this")
 
   class Error < StandardError; end
 
@@ -26,7 +27,7 @@ def self.get_local(title, year)
   end
 
   def self.search!(query)
-    json = JSON.parse(`should-i-watch-this lookup -f json #{query} -l`)
+    json = JSON.parse(`#{CLI_BIN} lookup -f json #{query} -l`)
 
     if error = json["error"]
       Rails.logger.error("event=movie_search_error error=#{error.inspect}")