btmgmt: Add "monitor" btmgmt submenu and command "features"

btmgmt: Add "monitor" btmgmt submenu and command "features"

This patch introduces a new submenu "monitor" along with command
‘features’ to help user query for supported advertisement features. The
command will work with the new MGMT opcode
MGMT_OP_READ_ADV_MONITOR_FEATURES.

Tested on Atlas Chromebook with a sample stdout below:
[mgmt]# features
Supported features:
        None
Enabled features:
        None
Max number of handles: 32
Max number of patterns: 16
Handles list with 2 items:
        0x0001
        0x0002

Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>