sonic-utilities [PoE] Add PoE CLI

What I did

Add show/config commands
Add UT
Update command reference

How I did it

Added ./config/plugins/poe.py that handles config commands:

config poe interface status <ifname> {enable|disable}
config poe interface priority <ifname> {low|high|crit}
config poe interface power-limit <ifname> <power>

Added ./show/plugins/poe.py that handles show commands:

show poe status
show poe pse status
show poe interface status [ifname]
show poe interface configuration [ifname]

Added ./tests/poe_test.py UT for the show commands.

How to verify it

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

NA

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

config commands example:

config poe interface status Ethernet0 enable
config poe interface priority Ethernet0 high
config poe interface power-limit Ethernet0 20.4

show poe status

  Id    PoE ports  Total power    Power consump    Power available    Power limit mode    HW info    Version
----  -----------  -------------  ---------------  -----------------  ------------------  ---------  ---------
   0            2  100.000 W      10.000 W         90.000 W           port                mcu1       0.1.2.3
   1            1  100.000 W      10.000 W         90.000 W           class               mcu2       0.1.2.3

show poe pse status

  Id  Status    Temperature    SW ver            HW ver
----  --------  -------------  ----------------  ----------------
   0  active    25.000 C       0.1.2.3           4.5.6.7
   1  active    25.000 C       0.1.2.3           4.5.6.7
   2  active    25.000 C       0.1.2.3           4.5.6.7

show poe interface status

Port         Status      En/Dis    Priority    Protocol          Class A    Class B  PWR Consump    PWR limit    Voltage    Current
-----------  ----------  --------  ----------  --------------  ---------  ---------  -------------  -----------  ---------  ---------
Ethernet0    delivering  enable    crit        802.3bt Type 3          2          4  10.000 W       50.000 W     50.000 V   0.200 A
Ethernet1    delivering  enable    high        802.3bt Type 3          2          4  10.000 W       50.000 W     50.000 V   0.200 A
Ethernet2    delivering  enable    low         802.3bt Type 3          2          4  10.000 W       50.000 W     50.000 V   0.200 A

show poe interface configuration

Port         En/Dis      Power limit  Priority
-----------  --------  -------------  ----------
Ethernet0    enable               50  crit
Ethernet1    enable               50  high
Ethernet2    enable               50  low