pimd,yang: Implement AutoRP CLI and NB config path

pimd,yang: Implement AutoRP CLI and NB config path

New CLI commands added:
router pim [vrf NAME]
  autorp discovery
  autorp announce RP-ADDR [GROUP | group-list PREFIX-LIST]
  autorp announce {scope (1-255) | interval (1-65535) | holdtime (0-65535)}

autorp discovery
  Enables Auto RP discovery for learning dynamic RP information using the
  AutoRP protocol.

autorp announce RP-ADDR [GROUP | group-list PREFIX-LIST]
  Enable announcements of a candidate RP with the given group range, or
  prefix list of group ranges, to an AutoRP mapping agent.

autorp announce {scope (1-255) | interval (1-65535) | holdtime (0-65535)}
  Configure the parameters of the AutoRP announcement messages.
  The scope sets the packet TTL.
  The interval sets the time between TX of announcements.
  The holdtime sets the hold time in the message, the time the mapping
  agent should wait before invalidating the candidate RP information.

debug pim autorp
  Enable debug logging of the AutoRP protocol

show ip pim [vrf NAME] autorp [json]
  Show details of the AutoRP protocol.
  To view learned RP info, use the existing command 'show ip pim rp-info'

Extend pim yang for new configuration:
  augment /frr-rt:routing/frr-rt:control-plane-protocols/frr-rt:control-plane-protocol/frr-pim:pim/frr-pim:address-family:
    +--rw rp
       +--rw auto-rp
          +--rw discovery-enabled?   boolean
          +--rw announce-scope?      uint8
          +--rw announce-interval?   uint16
          +--rw announce-holdtime?   uint16
          +--rw candidate-rp-list* [rp-address]
             +--rw rp-address           inet:ip-address
             +--rw (group-or-prefix-list)?
                +--:(group)
                |  +--rw group?         frr-route-types:ip-multicast-group-prefix
                +--:(prefix-list)
                   +--rw prefix-list?   plist-ref

Signed-off-by: Nathan Bahr <nbahr@atcorp.com>