Add file input plugin and grok parser (#4332)

plugins/inputs/file/dev/docker-compose.yml

@@ -0,0 +1,13 @@
+version: '3'
+
+services:
+  telegraf:
+      image: glinton/scratch
+      volumes:
+        - ./telegraf.conf:/telegraf.conf
+        - ../../../../telegraf:/telegraf
+        - ./json_a.log:/var/log/test.log
+      entrypoint:
+        - /telegraf
+        - --config
+        - /telegraf.conf

plugins/inputs/file/dev/json_a.log

@@ -0,0 +1,14 @@
+{
+"parent": {
+	"child": 3.0,
+	"ignored_child": "hi"
+},
+"ignored_null": null,
+"integer": 4,
+"list": [3, 4],
+"ignored_parent": {
+	"another_ignored_null": null,
+	"ignored_string": "hello, world!"
+},
+"another_list": [4]
+}

plugins/inputs/file/dev/telegraf.conf

@@ -0,0 +1,7 @@
+[[inputs.file]]
+  files = ["/var/log/test.log"]
+  data_format = "json"
+  name_override = "json_file"
+
+[[outputs.file]]
+  files = ["stdout"]