main: Add focus-on-file-open configuration option

If org.gnome.totem focus-on-file-open is false, then the application
will not raise focus when a new file is opened while the application is
already running in the background.

This enables the use case of quickly opening files from a file manager
with a keyboard in rapid succession: repeatedly pressing down,enter is
easier and quicker than repeatedly pressing down,enter,alt+tab
2 jobs for focus-on-file-open in 11 minutes and 29 seconds
latest
Status Job ID Name Coverage
  Test
passed #1243201
build-fedora

00:06:39

passed #1243202
flatpak
flatpak:master

00:11:28