Add policy as tag=value on pms

[mariotoffia]

So one may have the ability to write:

type MyStruct struct  {
  MyField string `pms:"test, expires:2021-02-17T08:10:12.000Z"`
}

This would generate a a policy for the parameter test as follows:

{
   "Type":"Expiration",
   "Version":"1.0",
   "Attributes":{
      "Timestamp":"2018-12-02T21:34:33.000Z"
   }
}

This would apply for any standard policy such as:

• ExpirationNotification
• NoChangeNotification

Since Policys are only for advanced parameters this would yield automatically that the parameter is converted as advanced even if the default tier is set as standard.