Add script processor (elastic#10850)

The script processor executes Javascript code to process an event. The processor uses a pure
Go implementation of ECMAScript 5.1. This can be useful in situations where one of the other
processors doesn’t provide the functionality you need to filter events.

The processor can be configured by embedding Javascript in your configuration file or by pointing
the processor at external file(s). See the included documentation for the full details.

    processors:
    - script:
        type: javascript
        code: >
          function process(event) {
              event.Tag("js");
          }

For observability it can add metrics with a histogram of the execution time and a counter
for the number of exceptions that occur.

There is an optional timeout configuration option to the processor that will
timeout the execution by interrupting the JS code.

Rather than have libbeat force the inclusion of the script processor in all Beats, make each Beat opt into the processor. It is imported by the log processing Beats (filebeat, journalbeat, and winlogbeat).

Benchmark Results

Here's a benchmark to get a rough idea of how long it takes to process an event in the processor's runtime

I updated the benchmark to test each case with and without the timeout enabled.

    BenchmarkBeatEventV0/Put-12                         2000000           707 ns/op
    BenchmarkBeatEventV0/timeout_Put-12                 1000000          1510 ns/op
    BenchmarkBeatEventV0/Object_Put_Key-12              2000000           631 ns/op
    BenchmarkBeatEventV0/timeout_Object_Put_Key-12      1000000          1252 ns/op
    BenchmarkBeatEventV0/Get-12                         2000000           750 ns/op
    BenchmarkBeatEventV0/timeout_Get-12                 1000000          1495 ns/op
    BenchmarkBeatEventV0/Get_Undefined_Key-12           1000000          1039 ns/op
    BenchmarkBeatEventV0/timeout_Get_Undefined_Key-12   1000000          2108 ns/op
    BenchmarkBeatEventV0/fields_get_key-12              2000000          1044 ns/op
    BenchmarkBeatEventV0/timeout_fields_get_key-12      1000000          2051 ns/op
    BenchmarkBeatEventV0/Get_@metadata-12               2000000           750 ns/op
    BenchmarkBeatEventV0/timeout_Get_@metadata-12       1000000          1745 ns/op
    BenchmarkBeatEventV0/Put_@metadata-12               1000000          1048 ns/op
    BenchmarkBeatEventV0/timeout_Put_@metadata-12       500000          2623 ns/op
    BenchmarkBeatEventV0/Delete_@metadata-12            2000000           842 ns/op
    BenchmarkBeatEventV0/timeout_Delete_@metadata-12    1000000          1629 ns/op
    BenchmarkBeatEventV0/Cancel-12                      2000000           759 ns/op
    BenchmarkBeatEventV0/timeout_Cancel-12              1000000          1329 ns/op
    BenchmarkBeatEventV0/Tag-12                         1000000          1189 ns/op
    BenchmarkBeatEventV0/timeout_Tag-12                 1000000          1973 ns/op
    BenchmarkBeatEventV0/AppendTo-12                    2000000           644 ns/op
    BenchmarkBeatEventV0/timeout_AppendTo-12            1000000          1347 ns/op

cmd/root.go

@@ -22,6 +22,9 @@ import (
 
 	cmd "github.com/elastic/beats/libbeat/cmd"
 	"github.com/elastic/beats/libbeat/cmd/instance"
+
+	// Import the script processor.
+	_ "github.com/elastic/beats/libbeat/processors/script"
 )
 
 // Name of this beat