Add template processor (#6494)

plugins/processors/template/README.md

@@ -0,0 +1,26 @@
+# Template Processor
+
+The `template` processor applies a go template to tag, field, measurement and time values to create a new tag.
+
+Golang [Template Documentation]
+
+### Configuration
+
+```toml
+  # Concatenate two tags to create a new tag
+  [[processors.template]]
+     ## Tag to create
+     tag = "topic"
+     ## Template to create tag
+     # Note: Single quotes (') are used, so the double quotes (") don't need escaping (\")
+     template = '{{ .Tag "hostname" }}.{{ .Tag "level" }}'
+```
+
+### Example
+
+```diff
+- cpu,level=debug,hostname=localhost value=42i
++ cpu,level=debug,hostname=localhost,topic=localhost.debug value=42i
+```
+
+[Template Documentation]:https://golang.org/pkg/text/template/