[chore][samplereceiver] Update internal telemetry metric units (#10672)

#### Description
Update telemetry units to be more clear. Related to
#10658, we
may be blocked here waiting for official units to use.

Note: I've kept [one
metric](https://github.com/open-telemetry/opentelemetry-collector/blob/7d5b1ba387e4e171e25bfeea9b70d6fdfbe08fab/cmd/mdatagen/internal/samplereceiver/metadata.yaml#L110)
with the unit "1", as it's not meant to be meaningful, just to show a
metric that's disabled by default.

Since this code is internal and only used for tests, from what I can
tell, I don't believe we need a changelog entry.

#### Link to tracking issue
Fixes
#10653

Author: crobert-1

cmd/mdatagen/internal/samplereceiver/documentation.md

@@ -123,7 +123,7 @@ Number of times the batch was sent due to a size trigger
 
 | Unit | Metric Type | Value Type | Monotonic |
 | ---- | ----------- | ---------- | --------- |
-| 1 | Sum | Int | true |
+| {times} | Sum | Int | true |
 
 ### otelcol_process_runtime_total_alloc_bytes
 
@@ -141,7 +141,7 @@ For example this metric only exists if feature A is enabled.
 
 | Unit | Metric Type | Value Type |
 | ---- | ----------- | ---------- |
-| 1 | Gauge | Int |
+| {items} | Gauge | Int |
 
 ### otelcol_request_duration
 

cmd/mdatagen/internal/samplereceiver/internal/metadata/generated_telemetry.go

@@ -155,7 +155,7 @@ telemetry:
     batch_size_trigger_send:
       enabled: true
       description: Number of times the batch was sent due to a size trigger
-      unit: "1"
+      unit: "{times}"
       sum:
         value_type: int
         monotonic: true
@@ -178,7 +178,7 @@ telemetry:
       enabled: true
       description: This metric is optional and therefore not initialized in NewTelemetryBuilder.
       extended_documentation: For example this metric only exists if feature A is enabled.
-      unit: "1"
+      unit: "{items}"
       optional: true
       gauge:
         async: true

cmd/mdatagen/internal/samplereceiver/metadata.yaml

@@ -32,7 +32,7 @@ func TestComponentTelemetry(t *testing.T) {
 		{
 			Name:        "otelcol_batch_size_trigger_send",
 			Description: "Number of times the batch was sent due to a size trigger",
-			Unit:        "1",
+			Unit:        "{times}",
 			Data: metricdata.Sum[int64]{
 				Temporality: metricdata.CumulativeTemporality,
 				IsMonotonic: true,
@@ -65,7 +65,7 @@ func TestComponentTelemetry(t *testing.T) {
 		{
 			Name:        "otelcol_batch_size_trigger_send",
 			Description: "Number of times the batch was sent due to a size trigger",
-			Unit:        "1",
+			Unit:        "{times}",
 			Data: metricdata.Sum[int64]{
 				Temporality: metricdata.CumulativeTemporality,
 				IsMonotonic: true,
@@ -93,7 +93,7 @@ func TestComponentTelemetry(t *testing.T) {
 		{
 			Name:        "otelcol_queue_length",
 			Description: "This metric is optional and therefore not initialized in NewTelemetryBuilder.",
-			Unit:        "1",
+			Unit:        "{items}",
 			Data: metricdata.Gauge[int64]{
 				DataPoints: []metricdata.DataPoint[int64]{
 					{

cmd/mdatagen/internal/samplereceiver/metrics_test.go

@@ -236,7 +236,7 @@ func TestLoadMetadata(t *testing.T) {
 						"batch_size_trigger_send": {
 							Enabled:     true,
 							Description: "Number of times the batch was sent due to a size trigger",
-							Unit:        strPtr("1"),
+							Unit:        strPtr("{times}"),
 							Sum: &sum{
 								MetricValueType: MetricValueType{pmetric.NumberDataPointValueTypeInt},
 								Mono:            Mono{Monotonic: true},
@@ -267,7 +267,7 @@ func TestLoadMetadata(t *testing.T) {
 							Enabled:               true,
 							Description:           "This metric is optional and therefore not initialized in NewTelemetryBuilder.",
 							ExtendedDocumentation: "For example this metric only exists if feature A is enabled.",
-							Unit:                  strPtr("1"),
+							Unit:                  strPtr("{items}"),
 							Optional:              true,
 							Gauge: &gauge{
 								MetricValueType: MetricValueType{