ucentral-schema: add support for configuring snmpd service using ucentral. WIFI-14152

[fjamarquez]

These changes make it possible to configure the snmpd service from the json file.

Example:

   "snmpd": {
    "agent": {
	"agentaddress": "UDP:161"
    },
        "access": {
	"private_access": {
                   "context": "none",
                   "group": private",
                   "level": "noauth",
                   "notify": "none",
                   "prefix": "exact",
                   "read": "all",
                   "version": "any",
                   "write": "none"
            },
	"public_access": {
                   "context": "none",                                                                
                   "group": "public",                                                                 
                   "level": "noauth",                                                                
                   "notify": "none",                                                                 
                   "prefix": "exact",                                                                
                   "read": "all",                                                                    
                   "version": "any",                                                                 
                   "write": "none"                                                                   
            } 
    },
        "agentx": {
            "type": "master"
        },
        "com2sec": {
            "public": {
                    "community": "public",
                    "secname": "ro",
                    "source": "default"
             },
             "private": {
                    "community": "private",
                    "secname": "rw",
                    "source": "default"
             }
        },
        "general": {
            "enabled": true,
        },
        "pass": [
            {                               
                    "miboid": ".1.3.6.1.1",
                    "name": "pass protocl",
                    "prog": "/bin/ash /etc/snmp/script.sh"
            },                       
        ], 
        "group": {
            "private_v2c": {
                    "group": "private",
                    "secname": "rw",
                    "version": "v2c"
            },
            "public_v2c": {
                    "group": "public",
                    "secname": "ro",
                    "version": "v2c"
             }
        },
        "system": {
            "sysContact": "company.com",
            "sysLocation": "Spain",
            "sysName": "Host1"
        },
        "view": {
            "all": {
                    "oid": ".1",
                    "type": "included",
                    "viewname": "all"
             }
        }
    }