01_Application_Framework: Further clarify some bits about D-Bus

01_Application_Framework: Further clarify some bits about D-Bus

This clarifies some bits about D-Bus as being in deprecation phase and
that gRPC should be used instead.

Bug-AGL: SPEC-4700
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: Iec494e165db2b40586a285117dd9f8b0a38971b0
(cherry picked from commit 9910e432faad988d4195c875d2cfb2700f16dec4)
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/28539
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>