policy api doc for review only

@croche-okta @wdawson-okta @srinivasanagandla-okta @stsai-okta @lboyette-okta @hoanguyen-okta @karlmcguinness-okta @cwu-okta @tthompson-okta

This is the doc review for the policy api. This is a new doc. Please look at it carefully, because I think a lot of things might need adjustments. Since this isn't in postman yet, I didn't have the objects for the reponses. If it's too much text to add, we can meet about it.
typo: `the` should be `they have a higher priority than the default rule`