Add dedup processor (#6792)

plugins/processors/dedup/README.md

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+# Dedup Processor Plugin
+
+If a metric sends the same value over successive intervals, suppress sending
+the same value to the TSD until this many seconds have elapsed.  This helps
+graphs over narrow time ranges still see timeseries with suppressed datapoints.
+
+This feature can be used to reduce traffic when metric's value does not change over
+time while maintain proper precision when value gets changed rapidly
+
+### Configuration
+
+```toml
+[[processors.dedup]]
+  ## Maximum time to suppress output
+  dedup_interval = "600s"
+```
+