docs: document summary settings and string_patterns configuration

Add the "summary" config key to the collector configuration docs
so that users can discover and configure summary metric tracking.
The summary feature was previously undocumented in the config
reference, making it difficult for users to learn about it without
reading the source code.

Update the example summary YAML to include a string_patterns section
demonstrating how to capture gvfs-helper curl error values, and
update the example output to show the array format used by
string_patterns fields.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: derrickstolee

Docs/Examples/summary_example.yml

@@ -31,6 +31,15 @@ region_timers:
     count_field: "batchCount"
     time_field: "batchTime"
 
+# String pattern rules - capture values from data events matching
+# a (category, key prefix) pair. Matched values are promoted into
+# the summary regardless of detail level or nesting.
+string_patterns:
+  # Capture curl/http error details from gvfs-helper
+  - category: "gvfs-helper"
+    key_prefix: "error/"
+    field_name: "gvfs_helper_errors"
+
 # Example output in OTEL span attributes:
 # {
 #   "trace2.process.summary": {
@@ -41,6 +50,7 @@ region_timers:
 #     "getCount": 127,
 #     "getTime": 50.3,
 #     "batchCount": 1,
-#     "batchTime": 12.3
+#     "batchTime": 12.3,
+#     "gvfs_helper_errors": ["(curl:35) SSL connect error [hard_fail]"]
 #   }
 # }

Docs/configure-custom-collector.md

@@ -46,6 +46,7 @@ receivers:
     pipe:   <windows-named-pipe-pathname>
     pii:    <pii-settings-pathname>
     filter: <filter-settings-pathname>
+    summary: <summary-settings-pathname>
 ```
 
 For example:
@@ -57,6 +58,7 @@ receivers:
     pipe:   "//./pipe/my-collector.pipe"
     pii:    "/usr/local/my-collector/pii.yml"
     filter: "/usr/local/my-collector/filter.yml"
+    summary: "/usr/local/my-collector/summary.yml"
 ```
 
 ### `<unix-domain-socket-pathname>` (Required on Unix)
@@ -117,3 +119,17 @@ generated OTEL telemetry data.  This is optional.  If omitted,
 summary-level telemetry will be emitted.
 
 See [config filter settings](./config-filter-settings.md) for details.
+
+### `<summary-settings-pathname>` (Optional)
+
+The pathname to a `summary.yml` file controlling which trace2 events
+are aggregated and promoted into the `trace2.process.summary` attribute
+on the OTEL process span.  This is optional.  If omitted, no summary
+metrics are emitted.
+
+The summary is emitted at all detail levels (including `dl:summary`),
+making it useful for surfacing important data without requiring verbose
+telemetry.
+
+See the [summary example](./Examples/summary_example.yml) for a
+complete example configuration.