[202012][dhcp-relay] Add support for dhcp_relay config cli

[yaqiangz]

Why I did it

Currently the config cli of dhcpv4 is may cause confusion and config of dhcpv6 is missing.

How I did it

Add dhcp_relay config cli and test cases.

config dhcp_relay ipv4 helper (add | del) <vlan_id> <helper_ip_list>
config dhcp_relay ipv6 destination (add | del) <vlan_id> <destination_ip_list>

How to verify it

1. Verify by unitest, all passed

2023-01-31T17:13:39.5310534Z ----------- coverage: platform linux, python 3.7.3-final-0 -----------
2023-01-31T17:13:39.5311171Z Name                                          Stmts   Miss  Cover
2023-01-31T17:13:39.5311934Z -----------------------------------------------------------------
2023-01-31T17:13:39.5318510Z config/dhcp_relay.py                            101     11    89%
2023-01-31T17:13:39.5375220Z utilities_common/dhcp_relay_util.py               7      0   100%
2023-01-31T17:13:39.5378676Z -----------------------------------------------------------------
2023-01-31T17:13:39.5379423Z Coverage HTML written to dir htmlcov
2023-01-31T17:13:39.5379772Z Coverage XML written to file coverage.xml
Coverage HTML written to dir htmlcov
Coverage XML written to file coverage.xml

2. Build sonic-utilities and install in DUT and run cli, test cli

admin@str-e1031-acs-3:~$ sudo config dhcp_relay ipv6 destination add 1000 fc02:2000::6    
Added DHCP relay address [fc02:2000::6] to Vlan1000
Restarting DHCP relay service...
admin@str-e1031-acs-3:~$ sudo config dhcp_relay ipv6 destination add 1000 fc02:2000::7 fc02:2000::8
Added DHCP relay address [fc02:2000::7,fc02:2000::8] to Vlan1000
Restarting DHCP relay service...
admin@str-e1031-acs-3:~$ show dhcprelay_helper ipv6                                                
--------  ------------
Vlan1000  fc02:2000::1
          fc02:2000::2
          fc02:2000::3
          fc02:2000::4
          fc02:2000::6
          fc02:2000::7
          fc02:2000::8
--------  ------------
admin@str-e1031-acs-3:~$ sudo config dhcp_relay ipv6 destination del 1000 fc02:2000::6   
Removed DHCP relay address [fc02:2000::6] from Vlan1000
Restarting DHCP relay service...
admin@str-e1031-acs-3:~$ sudo config dhcp_relay ipv6 destination del 1000 fc02:2000::7 fc02:2000::8   
Removed DHCP relay address [fc02:2000::7,fc02:2000::8] from Vlan1000
Restarting DHCP relay service...
admin@str-e1031-acs-3:~$ show dhcprelay_helper ipv6                                                
--------  ------------
Vlan1000  fc02:2000::1
          fc02:2000::2
          fc02:2000::3
          fc02:2000::4
--------  ------------

admin@str-e1031-acs-3:~$ sudo config dhcp_relay ipv4 helper add 1000 192.0.0.49
Added DHCP relay address [192.0.0.49] to Vlan1000
Restarting DHCP relay service...
admin@str-e1031-acs-3:~$ sudo config dhcp_relay ipv4 helper add 1000 192.0.0.50 192.0.0.51
Added DHCP relay address [192.0.0.50,192.0.0.51] to Vlan1000
Restarting DHCP relay service...
admin@str-e1031-acs-3:~$ sudo config dhcp_relay ipv4 helper del 1000 192.0.0.49   
Removed DHCP relay address [192.0.0.49] from Vlan1000
Restarting DHCP relay service...
admin@str-e1031-acs-3:~$ sudo config dhcp_relay ipv4 helper del 1000 192.0.0.49
Usage: config dhcp_relay ipv4 helper del [OPTIONS] <vid> DHCP_RELAY_HELPERS...
Try "config dhcp_relay ipv4 helper del -h" for help. Error: 192.0.0.49 is not a DHCP relay for Vlan1000
admin@str-e1031-acs-3:~$ sudo config dhcp_relay ipv4 helper del 1000 192.0.0.50 192.0.0.51   
Removed DHCP relay address [192.0.0.50,192.0.0.51] from Vlan1000
Restarting DHCP relay service...

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)

[yaqiangz]

@kellyyeh @jcaiMR @Blueve Could you please help to review this PR?