res_stasis: Expose event for call forwarding and follow forwarded channel.

This change adds an event for when an originated call is redirected to
another target. This event contains the original channel and the newly
created channel. If a stasis subscription exists on the original originated
channel for a stasis application then a new subscription will also be
created on the stasis application to the redirected channel. This allows
the application to follow the call path completely.

(closes issue ASTERISK-22719)
Reported by: Joshua Colp

Review: https://reviewboard.asterisk.org/r/3054/
........

Merged revisions 403808 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403810 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/ari/ari_model_validators.h

@@ -790,6 +790,24 @@ int ast_ari_validate_device_state_changed(struct ast_json *json);
  */
 ari_validator ast_ari_validate_device_state_changed_fn(void);
 
+/*!
+ * \brief Validator for Dial.
+ *
+ * Dialing state has changed.
+ *
+ * \param json JSON object to validate.
+ * \returns True (non-zero) if valid.
+ * \returns False (zero) if invalid.
+ */
+int ast_ari_validate_dial(struct ast_json *json);
+
+/*!
+ * \brief Function pointer to ast_ari_validate_dial().
+ *
+ * See \ref ast_ari_model_validators.h for more details.
+ */
+ari_validator ast_ari_validate_dial_fn(void);
+
 /*!
  * \brief Validator for EndpointStateChange.
  *
@@ -1187,6 +1205,16 @@ ari_validator ast_ari_validate_application_fn(void);
  * - application: string (required)
  * - timestamp: Date
  * - device_state: DeviceState (required)
+ * Dial
+ * - type: string (required)
+ * - application: string (required)
+ * - timestamp: Date
+ * - caller: Channel
+ * - dialstatus: string (required)
+ * - dialstring: string
+ * - forward: string
+ * - forwarded: Channel
+ * - peer: Channel (required)
  * EndpointStateChange
  * - type: string (required)
  * - application: string (required)