[AGNTLOG-618] Default file_scan_period to 1s (#49896)

### What does this PR do?

- Changes the default value of `logs_config.file_scan_period` from **10** seconds to **1** second.
- Updates `pkg/config/schema/core_schema.yaml` to match the new default.
- Adds a release note describing the change and how to opt out (slower scan) on hosts that need it.

### Motivation

The file log launcher uses this setting to schedule periodic filesystem scans for file-based log sources (new files, wildcards, rotation, and open-files selection). A 1 second default shortens the worst-case delay before the Agent discovers and starts tailing a new or rotated file. Deployments on slow or network-backed filesystems that need to limit metadata load can set `logs_config.file_scan_period` to a higher value in configuration.

### Describe how you validated your changes

- `inv test --targets=./pkg/config/setup` (all tests passed).

### Additional Notes

- This only affects the **file** log launcher’s scan cadence, not the idle read interval for an already open file.
- Users with an explicit `logs_config.file_scan_period` in `datadog.yaml` (or equivalent) are unchanged.


Co-authored-by: ryan.hall <ryan.hall@datadoghq.com>

Author: ddrthall

pkg/config/schema/core_schema.yaml

@@ -2253,7 +2253,7 @@ properties:
       file_scan_period:
         node_type: setting
         type: number
-        default: 10
+        default: 1
         tags:
         - golang_type:float64
       fingerprint_config:

pkg/config/setup/common_settings.go

@@ -1893,7 +1893,7 @@ func logsagent(config pkgconfigmodel.Setup) {
 	// could happen while serializing large objects on log lines.
 	config.BindEnvAndSetDefault("logs_config.aggregation_timeout", 1000)
 	// Time in seconds
-	config.BindEnvAndSetDefault("logs_config.file_scan_period", 10.0)
+	config.BindEnvAndSetDefault("logs_config.file_scan_period", 1.0)
 
 	// Controls how wildcard file log source are prioritized when there are more files
 	// that match wildcard log configurations than the `logs_config.open_files_limit`

releasenotes/notes/reduce-logs-file-scan-default-0204c0b75e19f3d0.yaml

@@ -0,0 +1,4 @@
+---
+enhancements:
+  - |
+    The default for ``logs_config.file_scan_period`` is now **1** second instead of 10, so the Agent discovers new and rotated log files on disk more quickly. Set ``logs_config.file_scan_period`` explicitly if you need a slower scan to reduce filesystem load (for example on network file systems).