[receiver/hostmetricsreceiver] cpu scraper - extract cpu count when m…

…etric is enabled (open-telemetry#32173)

**Description:** 
As described in
open-telemetry#32133
, in windows, the CPU count results of a wmi call with a hardcoded
context timeout of 3 seconds.
This leads to an error when the wmi is slow or system is under heavy
load, causing all the collected metrics to not be emitted.

The CPU count metrics, logical and physical, are not enabled by default
and there is no reason to calculate it unless it's enabled.

**Link to tracking Issue:** open-telemetry#32133

**Testing:** unit test has been validated
**Documentation:** <Describe the documentation added.>

Signed-off-by: Dani Louca <dlouca@splunk.com>
Co-authored-by: Antoine Toulme <antoine@lunar-ocean.com>

.chloggen/cpu-scraper.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: receiver/hostmetricsreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: do not extract the cpu count if the metric is not enabled; this will prevent unnecessary overhead, especially on windows
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [32133]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/cpu_scraper.go

@@ -74,17 +74,21 @@ func (s *scraper) scrape(ctx context.Context) (pmetric.Metrics, error) {
 		return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
 	}
 
-	numCPU, err := cpu.Counts(false)
-	if err != nil {
-		return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
+	if s.config.MetricsBuilderConfig.Metrics.SystemCPUPhysicalCount.Enabled {
+		numCPU, err := cpu.Counts(false)
+		if err != nil {
+			return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
+		}
+		s.mb.RecordSystemCPUPhysicalCountDataPoint(now, int64(numCPU))
 	}
-	s.mb.RecordSystemCPUPhysicalCountDataPoint(now, int64(numCPU))
 
-	numCPU, err = cpu.Counts(true)
-	if err != nil {
-		return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
+	if s.config.MetricsBuilderConfig.Metrics.SystemCPULogicalCount.Enabled {
+		numCPU, err := cpu.Counts(true)
+		if err != nil {
+			return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
+		}
+		s.mb.RecordSystemCPULogicalCountDataPoint(now, int64(numCPU))
 	}
-	s.mb.RecordSystemCPULogicalCountDataPoint(now, int64(numCPU))
 
 	if s.config.MetricsBuilderConfig.Metrics.SystemCPUFrequency.Enabled {
 		cpuInfos, err := s.getCPUInfo()