Enhance process event metrics (#653)

This adds sources info to process events in the metrics document.
```
        "process_events": {
          "sent_bytes": 1478944,
          "sent_count": 732,
          "sources": [
            {
              "sent_bytes": 0,
              "sent_count": 0,
              "source": "shmget",
              "suppressed_bytes": 0,
              "suppressed_count": 1
            }
          ],
          "suppressed_bytes": 0,
          "suppressed_count": 7
        }
```
This change allows for data based diag->prod decisions for new Linux
process events: load_module, ptrace, and shmget

Author: nicholasberlin

custom_documentation/doc/endpoint/metrics/metrics.md

@@ -75,6 +75,11 @@ This is an internal state management document that includes metrics on Endpoint'
 | Endpoint.metrics.documents_volume.overall.suppressed_count |
 | Endpoint.metrics.documents_volume.process_events.sent_bytes |
 | Endpoint.metrics.documents_volume.process_events.sent_count |
+| Endpoint.metrics.documents_volume.process_events.sources.sent_bytes |
+| Endpoint.metrics.documents_volume.process_events.sources.sent_count |
+| Endpoint.metrics.documents_volume.process_events.sources.source |
+| Endpoint.metrics.documents_volume.process_events.sources.suppressed_bytes |
+| Endpoint.metrics.documents_volume.process_events.sources.suppressed_count |
 | Endpoint.metrics.documents_volume.process_events.suppressed_bytes |
 | Endpoint.metrics.documents_volume.process_events.suppressed_count |
 | Endpoint.metrics.documents_volume.registry_events.sent_bytes |

custom_documentation/src/endpoint/data_stream/metrics/metrics.yaml

@@ -82,6 +82,11 @@ fields:
   - Endpoint.metrics.documents_volume.overall.suppressed_count
   - Endpoint.metrics.documents_volume.process_events.sent_bytes
   - Endpoint.metrics.documents_volume.process_events.sent_count
+  - Endpoint.metrics.documents_volume.process_events.sources.sent_bytes
+  - Endpoint.metrics.documents_volume.process_events.sources.sent_count
+  - Endpoint.metrics.documents_volume.process_events.sources.source
+  - Endpoint.metrics.documents_volume.process_events.sources.suppressed_bytes
+  - Endpoint.metrics.documents_volume.process_events.sources.suppressed_count
   - Endpoint.metrics.documents_volume.process_events.suppressed_bytes
   - Endpoint.metrics.documents_volume.process_events.suppressed_count
   - Endpoint.metrics.documents_volume.registry_events.sent_bytes