[exporter/prometheus] Fix panic when mutating data (#29608)

The prometheus exporter hit a panic when accumulating `Delta` metrics
into `Cumulative` sums. This is because the exporter does not enable
mutating data in its capability. This change enables the exporter to
mutate data in a safe and supported way.

Fixed #29574

**Testing**
There are existing tests that hit the logic that was panicking, but the
metrics are set to `StateMutable` in testing (which is the only way they
can be created and setup for testing). I believe that means that before
this change the tests were invalid (didn't represent reality), but after
this change they'll properly represent the exporter's functionality.

.chloggen/fix_prometheus_panic.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: prometheusexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix panic when exporter mutates data
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [29574]
+
+# (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: []

exporter/prometheusexporter/factory.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/consumer"
 	"go.opentelemetry.io/collector/exporter"
 	"go.opentelemetry.io/collector/exporter/exporterhelper"
 
@@ -52,6 +53,7 @@ func createMetricsExporter(
 		prometheus.ConsumeMetrics,
 		exporterhelper.WithStart(prometheus.Start),
 		exporterhelper.WithShutdown(prometheus.Shutdown),
+		exporterhelper.WithCapabilities(consumer.Capabilities{MutatesData: true}),
 	)
 	if err != nil {
 		return nil, err

exporter/prometheusexporter/go.mod

@@ -16,6 +16,7 @@ require (
 	go.opentelemetry.io/collector/config/confighttp v0.90.2-0.20231201205146-6e2fdc755b34
 	go.opentelemetry.io/collector/config/configtls v0.90.2-0.20231201205146-6e2fdc755b34
 	go.opentelemetry.io/collector/confmap v0.90.2-0.20231201205146-6e2fdc755b34
+	go.opentelemetry.io/collector/consumer v0.90.2-0.20231201205146-6e2fdc755b34
 	go.opentelemetry.io/collector/exporter v0.90.2-0.20231201205146-6e2fdc755b34
 	go.opentelemetry.io/collector/pdata v1.0.1-0.20231201205146-6e2fdc755b34
 	go.opentelemetry.io/collector/receiver v0.90.2-0.20231201205146-6e2fdc755b34
@@ -140,7 +141,6 @@ require (
 	go.opentelemetry.io/collector/config/configopaque v0.90.2-0.20231201205146-6e2fdc755b34 // indirect
 	go.opentelemetry.io/collector/config/configtelemetry v0.90.2-0.20231201205146-6e2fdc755b34 // indirect
 	go.opentelemetry.io/collector/config/internal v0.90.2-0.20231201205146-6e2fdc755b34 // indirect
-	go.opentelemetry.io/collector/consumer v0.90.2-0.20231201205146-6e2fdc755b34 // indirect
 	go.opentelemetry.io/collector/extension v0.90.2-0.20231201205146-6e2fdc755b34 // indirect
 	go.opentelemetry.io/collector/extension/auth v0.90.2-0.20231201205146-6e2fdc755b34 // indirect
 	go.opentelemetry.io/collector/featuregate v1.0.1-0.20231201205146-6e2fdc755b34 // indirect