chat-view: Add support for selecting multiple files

This is currently unused, but shall be used when MMS support
has landed
7 jobs for wip/sadiq/attachment in 12 minutes and 30 seconds (queued for 2 minutes and 18 seconds)
Status Job ID Name Coverage
  Build
passed #368996
librem5
build-pureos-gcc-byzantium

00:03:32

 
  Test
passed #368998
librem5
check-po

00:00:25

passed #368997
librem5
test:debian-gcc

00:02:58

21.6%
 
  Package
passed #368999
librem5
package-pureos-byzantium

00:01:50

passed #369000
librem5:arm64
package-pureos-byzantium:arm64

00:05:34

 
  Test Package
passed #369001
librem5
autopkgtest-pureos-byzantium-package

00:01:19

passed #369002
librem5
lintian-pureos-byzantium-package

00:00:51