[configlet] Duplicate Helpers IP Configuration

[d-dashkov]

- What I did
Fixed duplicate IP addresses when configure DHCP relay using configlets that has duplicate helper IPs.
fixes sonic-net/sonic-buildimage#6559
Also it works with dublicate IP addresses in MGMT_INTERFACE.*.forced_mgmt_routes.

- How I did it
Check the input configuration with YANG models, (in case the modes do not exist, find duplicates and remove them).

- How to verify it
DHCP_SRVERS

Create configlet.json with content:
[
{
	"VLAN": {
		"Vlan1000": {
			"dhcp_servers": ["192.0.0.6", "192.0.0.6", "192.0.0.6", "192.0.0.8"]
		}
	}
}
]

Run the following CLI commands:
configlet -j ./configlet.json -u

Duplicated instance of "dhcp_servers" leaf-list ("192.0.0.6").

MGMT_INTERFACE

Create mg_configlet.json with content:
[
{
    "MGMT_INTERFACE": {
        "eth0|192.168.111.214/24": {
		    "forced_mgmt_routes": [
				"10.0.0.100/31",
				"10.0.0.100/31",
				"10.250.0.8",
				"10.0.0.100/31",
				"10.255.0.0/28"
			],
            "gwaddr": "192.168.111.3"
        }
    }
}
]

Run the following CLI commands:
configlet -j ./mg_configlet.json -u

Note: Below table(s) have no YANG models:
MGMT_INTERFACE,
Duplicate found: 10.0.0.100/31
Duplicate found: 10.0.0.100/31

show runningconfiguration all

"eth0|192.168.111.214/24": {
	"forced_mgmt_routes": [
		"10.0.0.100/31",
		"10.250.0.8",
		"10.255.0.0/28"
	],
	"gwaddr": "192.168.111.3"
}

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

Duplicated instance of "" leaf-list 
Duplicate found: 192.0.0.6

Signed-off-by: d-dashkov Dmytro_Dashkov@Jabil.com

[d-dashkov]

retest this please