Test(generic-metrics): Add tests for process message flow for generic metrics pipeline (#55950)

### Overview

Adds an additional test for process_message where it is on the generic
metrics pipeline (before it is only on the release health pipeline)

Author: john-z-yang

pyproject.toml

@@ -865,7 +865,6 @@ module = [
     "tests.sentry.sentry_metrics.limiters.test_writes_limiter",
     "tests.sentry.sentry_metrics.test_base_indexer",
     "tests.sentry.sentry_metrics.test_batch",
-    "tests.sentry.sentry_metrics.test_multiprocess_steps",
     "tests.sentry.snuba.metrics.test_snql",
     "tests.sentry.snuba.test_tasks",
     "tests.sentry.tagstore.test_types",

src/sentry/sentry_metrics/configuration.py

@@ -98,7 +98,7 @@ def get_ingest_config(
             )
         )
 
-    if db_backend == IndexerStorage.MOCK:
+    if (use_case_key, db_backend) == (UseCaseKey.RELEASE_HEALTH, IndexerStorage.MOCK):
         _register_ingest_config(
             MetricsIngestConfiguration(
                 db_backend=IndexerStorage.MOCK,
@@ -108,13 +108,30 @@ def get_ingest_config(
                 use_case_id=use_case_key,
                 internal_metrics_tag="release-health",
                 writes_limiter_cluster_options={},
-                writes_limiter_namespace="test-namespace",
+                writes_limiter_namespace="test-namespace-rh",
                 cardinality_limiter_cluster_options={},
                 cardinality_limiter_namespace=RELEASE_HEALTH_PG_NAMESPACE,
                 should_index_tag_values=True,
             )
         )
 
+    if (use_case_key, db_backend) == (UseCaseKey.PERFORMANCE, IndexerStorage.MOCK):
+        _register_ingest_config(
+            MetricsIngestConfiguration(
+                db_backend=IndexerStorage.MOCK,
+                db_backend_options={},
+                input_topic="topic",
+                output_topic="output-topic",
+                use_case_id=use_case_key,
+                internal_metrics_tag="perf",
+                writes_limiter_cluster_options={},
+                writes_limiter_namespace="test-namespace-perf",
+                cardinality_limiter_cluster_options={},
+                cardinality_limiter_namespace=PERFORMANCE_PG_NAMESPACE,
+                should_index_tag_values=False,
+            )
+        )
+
     return _METRICS_INGEST_CONFIG_BY_USE_CASE[(use_case_key, db_backend)]