[chore][confmap] Show that issue 10799 is fixed (#10809)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

<!-- Issue number if applicable -->

Shows that #10795 (as well as #10800) fixed this issue.

#### Link to tracking issue

Fixes #10799

Author: mx-psi

confmap/internal/e2e/testdata/indirect-slice-env-var-main.yaml

@@ -0,0 +1,13 @@
+receivers:
+  nop:
+  otlp:
+    protocols:
+      grpc:
+
+exporters:
+  nop:
+  otlp:
+    endpoint: localhost:4317
+
+service:
+  pipelines: ${file:${env:BASE_FOLDER}/indirect-slice-env-var-pipelines.yaml}

confmap/internal/e2e/testdata/indirect-slice-env-var-pipelines.yaml

@@ -0,0 +1,3 @@
+logs:
+  receivers: ${env:OTEL_LOGS_RECEIVER}
+  exporters: ${env:OTEL_LOGS_EXPORTER}

confmap/internal/e2e/types_test.go

@@ -634,3 +634,54 @@ logging:
 		cfgStr.Field,
 	)
 }
+
+func TestIndirectSliceEnvVar(t *testing.T) {
+	previousValue := globalgates.StrictlyTypedInputGate.IsEnabled()
+	err := featuregate.GlobalRegistry().Set(globalgates.StrictlyTypedInputID, true)
+	require.NoError(t, err)
+	defer func() {
+		seterr := featuregate.GlobalRegistry().Set(globalgates.StrictlyTypedInputID, previousValue)
+		require.NoError(t, seterr)
+	}()
+
+	// This replicates the situation in https://github.com/open-telemetry/opentelemetry-collector/issues/10799
+	// where a configuration file is loaded that contains a reference to a slice of strings in an environment variable.
+	t.Setenv("BASE_FOLDER", "testdata")
+	t.Setenv("OTEL_LOGS_RECEIVER", "[nop, otlp]")
+	t.Setenv("OTEL_LOGS_EXPORTER", "[otlp, nop]")
+	resolver := NewResolver(t, "indirect-slice-env-var-main.yaml")
+	conf, err := resolver.Resolve(context.Background())
+	require.NoError(t, err)
+
+	type CollectorConf struct {
+		Exporters struct {
+			OTLP struct {
+				Endpoint string `mapstructure:"endpoint"`
+			} `mapstructure:"otlp"`
+			Nop struct{} `mapstructure:"nop"`
+		} `mapstructure:"exporters"`
+		Receivers struct {
+			OTLP struct {
+				Protocols struct {
+					GRPC struct{} `mapstructure:"grpc"`
+				} `mapstructure:"protocols"`
+			} `mapstructure:"otlp"`
+			Nop struct{} `mapstructure:"nop"`
+		} `mapstructure:"receivers"`
+		Service struct {
+			Pipelines struct {
+				Logs struct {
+					Exporters []string `mapstructure:"exporters"`
+					Receivers []string `mapstructure:"receivers"`
+				} `mapstructure:"logs"`
+			} `mapstructure:"pipelines"`
+		} `mapstructure:"service"`
+	}
+
+	var collectorConf CollectorConf
+	err = conf.Unmarshal(&collectorConf)
+	require.NoError(t, err)
+	assert.Equal(t, collectorConf.Exporters.OTLP.Endpoint, "localhost:4317")
+	assert.Equal(t, collectorConf.Service.Pipelines.Logs.Receivers, []string{"nop", "otlp"})
+	assert.Equal(t, collectorConf.Service.Pipelines.Logs.Exporters, []string{"otlp", "nop"})
+}