service: add thread.flush_on_shutdown option

This commit adds documentation for the new `thread.flush_on_shutdown`
configuration option in the SERVICE section.

When enabled, the engine waits for threaded input ring buffers to flush
during graceful shutdown, preventing data loss from threaded inputs.

refs: fluent/fluent-bit#11337

Signed-off-by: jinyong.choi <inimax801@gmail.com>

Author: jinyongchoi

administration/configuring-fluent-bit/classic-mode/configuration-file.md

@@ -21,6 +21,7 @@ The `Service` section defines global properties of the service. The following ke
 | --------------- | ------------- | ------------- |
 | `flush`           | Set the flush time in `seconds.nanoseconds`. The engine loop uses a Flush timeout to define when it's required to flush the records ingested by input plugins through the defined output plugins.  | `1` |
 | `grace`           | Set the grace time in `seconds` as an integer value. The engine loop uses a grace timeout to define wait time on exit. | `5` |
+| `thread.flush_on_shutdown` | If enabled, the engine waits for threaded input ring buffers to flush during graceful shutdown, preventing data loss from threaded inputs. Allowed values are: `on` and `off`. | `off` |
 | daemon          | Boolean. Determines whether Fluent Bit should run as a Daemon (background). Allowed values are: `yes`, `no`, `on`, and `off`. Don't enable when using a Systemd based unit, such as the one provided in Fluent Bit packages.  | `Off` |
 | `dns.mode`        | Set the primary transport layer protocol used by the asynchronous DNS resolver. Can be overridden on a per plugin basis. | `UDP` |
 | `log_file`        | Absolute path for an optional log file. By default all logs are redirected to the standard error interface (stderr). | _none_ |

administration/configuring-fluent-bit/yaml/service-section.md

@@ -6,6 +6,7 @@ The `service` section of YAML configuration files defines global properties of t
 | --- | ----------- | ------------- |
 | `flush` | Sets the flush time in `seconds.nanoseconds`. The engine loop uses a flush timeout to define when to flush the records ingested by input plugins through the defined output plugins. | `1` |
 | `grace` | Sets the grace time in `seconds` as an integer value. The engine loop uses a grace timeout to define the wait time on exit. | `5` |
+| `thread.flush_on_shutdown` | If enabled, the engine waits for threaded input ring buffers to flush during graceful shutdown, preventing data loss from threaded inputs. Accepted values: `off` or `on`. | `off` |
 | `daemon` | Specifies whether Fluent Bit should run as a daemon (background process). Possible values: `yes`, `no`, `on`, and `off`. Don't enable when using a Systemd-based unit, such as the one provided in Fluent Bit packages. | `off` |
 | `dns.mode` | Sets the primary transport layer protocol used by the asynchronous DNS resolver. Can be overridden on a per-plugin basis. | `UDP` |
 | `log_file` | Absolute path for an optional log file. By default, all logs are redirected to the standard error interface (`stderr`). | _none_ |