Add service input plugin for OpenConfig streaming telemetry (#2292)

plugins/inputs/jti_openconfig_telemetry/README.md

@@ -0,0 +1,59 @@
+# JTI OpenConfig Telemetry Input Plugin
+
+This plugin reads Juniper Networks implementation of OpenConfig telemetry data from listed sensors using Junos Telemetry Interface. Refer to
+[openconfig.net](http://openconfig.net/) for more details about OpenConfig and [Junos Telemetry Interface (JTI)](https://www.juniper.net/documentation/en_US/junos/topics/concept/junos-telemetry-interface-oveview.html).
+
+### Configuration:
+
+```toml
+# Subscribe and receive OpenConfig Telemetry data using JTI
+[[inputs.jti_openconfig_telemetry]]
+  ## List of device addresses to collect telemetry from
+  servers = ["localhost:1883"]
+
+  ## Authentication details. Username and password are must if device expects
+  ## authentication. Client ID must be unique when connecting from multiple instances
+  ## of telegraf to the same device
+  username = "user"
+  password = "pass"
+  client_id = "telegraf"
+
+  ## Frequency to get data
+  sample_frequency = "1000ms"
+
+  ## Sensors to subscribe for
+  ## A identifier for each sensor can be provided in path by separating with space
+  ## Else sensor path will be used as identifier
+  ## When identifier is used, we can provide a list of space separated sensors.
+  ## A single subscription will be created with all these sensors and data will
+  ## be saved to measurement with this identifier name
+  sensors = [
+   "/interfaces/",
+   "collection /components/ /lldp",
+  ]
+
+  ## We allow specifying sensor group level reporting rate. To do this, specify the
+  ## reporting rate in Duration at the beginning of sensor paths / collection
+  ## name. For entries without reporting rate, we use configured sample frequency
+  sensors = [
+   "1000ms customReporting /interfaces /lldp",
+   "2000ms collection /components",
+   "/interfaces",
+  ]
+
+  ## x509 Certificate to use with TLS connection. If it is not provided, an insecure
+  ## channel will be opened with server
+  ssl_cert = "/etc/telegraf/cert.pem"
+
+  ## Delay between retry attempts of failed RPC calls or streams. Defaults to 1000ms.
+  ## Failed streams/calls will not be retried if 0 is provided
+  retry_delay = "1000ms"
+
+  ## To treat all string values as tags, set this to true
+  str_as_tags = false
+```
+
+### Tags:
+
+- All measurements are tagged appropriately using the identifier information
+  in incoming data