Add option for spacer tile in dock between apps

[northportio]

It would be nice to automate the addition of spacer tiles in the dock. Like here

	<key>tile-data</key>
	<dict/>
	<key>tile-type</key>
	<string>spacer-tile</string>
</dict>
</plist>

It seems to just be a string in the plist for dock.

Also found this issue that shows dockutil has this function.

[stale[bot]]

This issue has been marked 'stale' due to lack of recent activity. If there is no further activity, the issue will be closed in another 30 days. Thank you for your contribution!

Please read this blog post to see the reasons why I mark issues as stale.

[stale[bot]]

This issue has been closed due to inactivity. If you feel this is in error, please reopen the issue or file a new issue with the relevant details.