Add :query-shell-command

[Sntx626]

I'd like to be able to run a shell command and have helix run the returned text of the shell command as an internal command.

The name for the command is just a suggestions.

I.e.:

helix

:query-shell-command /usr/bin/my-custom-script.sh

my-custom-script.sh

#!/bin/bash
DATE=$(date +'%Y-%m-%d')
FILENAME=~/Documents/journal/$DATE.md 

cat > $FILENAME <<EOL
# ${DATE} journal entry

<!--
## Notes
-->
EOL

echo ":open $FILENAME"

[the-mikedavis]

See #8636