[chore] [receiver/datadog] Add support for v1 series (#33957)

**Description:**
This PR adds support for V1 series, as well as batches the metrics by
resource, scope, and datapoint attributes. The batching code will also
be required for future PRs which will add support for v2 series
endpoints, service checks, and sketches.

Follow up of #33631 and #33922.

The full version of the code can be found in the
`cedwards/datadog-metrics-receiver-full` branch, or in Grafana Alloy:
https://github.com/grafana/alloy/tree/main/internal/etc/datadogreceiver

**Link to tracking Issue:** 
#18278 

**Testing:** 
Unit tests, as well as an end-to-end test, have been added.

---------

Co-authored-by: Federico Torres <federico.sa.torres@gmail.com>

receiver/datadogreceiver/batcher.go

@@ -0,0 +1,119 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package datadogreceiver // import "github.com/open-telemetry/opentelemetry-collector-contrib/receiver/datadogreceiver"
+
+import (
+	"go.opentelemetry.io/collector/pdata/pcommon"
+	"go.opentelemetry.io/collector/pdata/pmetric"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/exp/metrics/identity"
+)
+
+type Batcher struct {
+	pmetric.Metrics
+
+	resourceMetrics map[identity.Resource]pmetric.ResourceMetrics
+	scopeMetrics    map[identity.Scope]pmetric.ScopeMetrics
+	metrics         map[identity.Metric]pmetric.Metric
+}
+
+func newBatcher() Batcher {
+	return Batcher{
+		Metrics:         pmetric.NewMetrics(),
+		resourceMetrics: make(map[identity.Resource]pmetric.ResourceMetrics),
+		scopeMetrics:    make(map[identity.Scope]pmetric.ScopeMetrics),
+		metrics:         make(map[identity.Metric]pmetric.Metric),
+	}
+}
+
+// Dimensions stores the properties of the series that are needed in order
+// to unique identify the series. This is needed in order to batch metrics by
+// resource, scope, and datapoint attributes
+type Dimensions struct {
+	name          string
+	metricType    pmetric.MetricType
+	resourceAttrs pcommon.Map
+	scopeAttrs    pcommon.Map
+	dpAttrs       pcommon.Map
+	buildInfo     string
+}
+
+var metricTypeMap = map[string]pmetric.MetricType{
+	"count":         pmetric.MetricTypeSum,
+	"gauge":         pmetric.MetricTypeGauge,
+	"rate":          pmetric.MetricTypeSum,
+	"service_check": pmetric.MetricTypeGauge,
+	"sketch":        pmetric.MetricTypeExponentialHistogram,
+}
+
+func parseSeriesProperties(name string, metricType string, tags []string, host string, version string, stringPool *StringPool) Dimensions {
+	resourceAttrs, scopeAttrs, dpAttrs := tagsToAttributes(tags, host, stringPool)
+	return Dimensions{
+		name:          name,
+		metricType:    metricTypeMap[metricType],
+		buildInfo:     version,
+		resourceAttrs: resourceAttrs,
+		scopeAttrs:    scopeAttrs,
+		dpAttrs:       dpAttrs,
+	}
+}
+
+func (b Batcher) Lookup(dim Dimensions) (pmetric.Metric, identity.Metric) {
+	resource := dim.Resource()
+	resourceID := identity.OfResource(resource)
+	resourceMetrics, ok := b.resourceMetrics[resourceID]
+	if !ok {
+		resourceMetrics = b.Metrics.ResourceMetrics().AppendEmpty()
+		resource.MoveTo(resourceMetrics.Resource())
+		b.resourceMetrics[resourceID] = resourceMetrics
+	}
+
+	scope := dim.Scope()
+	scopeID := identity.OfScope(resourceID, scope)
+	scopeMetrics, ok := b.scopeMetrics[scopeID]
+	if !ok {
+		scopeMetrics = resourceMetrics.ScopeMetrics().AppendEmpty()
+		scope.MoveTo(scopeMetrics.Scope())
+		b.scopeMetrics[scopeID] = scopeMetrics
+	}
+
+	m := dim.Metric()
+	metricID := identity.OfMetric(scopeID, m)
+	metric, ok := b.metrics[metricID]
+	if !ok {
+		metric = scopeMetrics.Metrics().AppendEmpty()
+		m.MoveTo(metric)
+		b.metrics[metricID] = metric
+	}
+
+	return metric, metricID
+}
+
+func (d Dimensions) Resource() pcommon.Resource {
+	resource := pcommon.NewResource()
+	d.resourceAttrs.CopyTo(resource.Attributes()) // TODO(jesus.vazquez) review this copy
+	return resource
+}
+
+func (d Dimensions) Scope() pcommon.InstrumentationScope {
+	scope := pcommon.NewInstrumentationScope()
+	scope.SetName("otelcol/datadogreceiver")
+	scope.SetVersion(d.buildInfo)
+	d.scopeAttrs.CopyTo(scope.Attributes())
+	return scope
+}
+
+func (d Dimensions) Metric() pmetric.Metric {
+	metric := pmetric.NewMetric()
+	metric.SetName(d.name)
+	switch d.metricType {
+	case pmetric.MetricTypeSum:
+		metric.SetEmptySum()
+	case pmetric.MetricTypeGauge:
+		metric.SetEmptyGauge()
+	case pmetric.MetricTypeExponentialHistogram:
+		metric.SetEmptyExponentialHistogram()
+	}
+	return metric
+}