This commit introduces a new Kconfig symbol MCUMGR_SMP_BT_AUTHEN.
When selected it configures the Bluetooth mcumgr transport to require
an authenticated connection.
If the Bluetooth mcumgr transport is selected then this new symbol is
selected by default. Bluetooth SMP is also selected to ensure Zephyr
is configured with Bluetooth security features enabled to provide
Bluetooth authentication APIs to the user's app. Users can choose to
disable this level of security for the Bluetooth mcumgr transport if
they do not require it.
Fixes#16482
Signed-off-by: Nick Ward <nix.ward@gmail.com>
b5f335b11b