[image_config]: Update DHCP rate-limit (#17132)

Change DHCP rate limit in SONiC copp configuration to 100 PPS as this is
necessary to ensure that DHCP flood does not cause LACP/BGP flaps in all
scenarios

This is an extension to the change in image_config: copp: Enable rate limiting 
for bgp, lacp, dhcp, lldp, macsec and udld #14859 and sonic-mgmt change in 
[tests/copp]: Update copp mgmt tests to support new rate-limits sonic-mgmt#8199

Why I did it
300 PPS is not sufficient to prevent LACP/BGP flaps in all cases. 100 PPS seems to
provide better resiliency against DHCP traffic flood to CPU.

Microsoft ADO 25776614:

Send DHCP broadcast packets to DUT and verify that they are trapped to CPU at 100 PPS.

Signed-off-by: Prabhat Aravind <paravind@microsoft.com>

files/image_config/copp/copp_cfg.j2

@@ -34,8 +34,8 @@
 		    "queue": "4",
 		    "meter_type":"packets",
 		    "mode":"sr_tcm",
-		    "cir":"300",
-		    "cbs":"300",
+		    "cir":"100",
+		    "cbs":"100",
 		    "red_action":"drop"
 	    },
 	    "queue1_group1": {