[config/console] Support update console configuration related commands

[Blueve]

- What I did

• Support config console remote_device command
• Support config console baud command
• Support config console flow_control command

For more detail regarding the design, please refer to HLD(section 3.3.1.2.2/3.3.1.2.3/3.3.1.2.4): https://github.com/Azure/SONiC/blob/master/doc/console/SONiC-Console-Switch-High-Level-Design.md#3312-config

- How I did it

• Add new commands in console.py file to support update related config console commands
• Add UTs for new added commands

- How to verify it

1. UTs are all passed

---------- coverage: platform linux2, python 2.7.16-final-0 ----------
Name                                       Stmts   Miss  Cover
--------------------------------------------------------------
config/console.py                             94      1    99%

2. Tested on a physical SONiC DUT

Error handling:

sudo config console baud 2 9600
Usage: config console baud [OPTIONS] <line_number> <baud>
Try "config console baud -h" for help.

admin@sonic:~$ sudo config console remote_device 2 switch1
Usage: config console remote_device [OPTIONS] <line_number> <device_name>
Try "config console remote_device -h" for help.

Error: Given device name switch1 has been used. Please enter a valid device name or remove the existing one !!

Positive result:

admin@sonic:~$ sudo config console baud 1 115000
admin@sonic:~$ sudo config console remote_device 1 switch1
admin@sonic:~$ sudo config console flow_control enable 1
admin@sonic:~$ sudo config console flow_control disable 1

- Previous command output (if the output of a command-line utility has changed)

- New command output (if the output of a command-line utility has changed)