Add support for the following config options for opflex agent (with defaults shown)

[mchalla]

"opflex": {
//  // This section controls how persistant config is treated
//  // during opflex startup
    "startup": {
//      // Location of the pol.json that will be read and used on startup
//      // will be provided by the orchestrator, needs to be on a persistent volume
        "policy-file": "<location of the policy file>",
//      // How long to use the above file after agent connects to the leaf
//      // default is 0 meaning as soon as agent connects to leaf we will
//      // stop using the local policy for future resolves
        "policy-duration": 60,
//      // Wait till opflex connects to leaf before using the local policy
//      // default 0, use in combination with policy-duration > 0
//      // This is useful if you want to preserve the old flows until
//      // the leaf connection succeeds and not overwrite them before we
//      // connect to the leaf using the local policy
//      // A related knob timers.switch-sync-delay controls after connection
//      // how much more longer to freeze the flow tables
//      "resolve-aft-conn": false
//  },
   "timers": {
       // Initial switch sync delay
       // How long to wait from PlatformConfig resolution
       // to start the switch sync, default 5 seconds
       "switch-sync-delay":  5,
       // Subsequent switch sync delay
       // In case we have subsequent resolutions pending
       // whats the minimum time any resolution can be
       // pending before we retry switch sync
       // default 0, no further wait
       // If this value is > 0, we keep checking if
       // every pending MO waited at least this long
       // before retrying switch sync
       // Max retries will be 5 so as to not wait
       // forever
       "switch-sync-dynamic": 10