templates: Use help link widget in invite user modal.
templates: Use help link widget in invite user modal.

Updates the help center link in the invite user modal to use the
help_link_widget.

zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip