Add enablePrometheus annotation. (#30452)

* Add enablePrometheus annotation.

The PR adds the enablePrometheus annotation to load tests that are
part of PSM data plan performance tests. This annotation enables
all PSM related tests to obtain data from Prometehus, even for the
regular tests.

tools/internal_ci/linux/grpc_psm_performance_gke_experiment.sh

@@ -100,6 +100,7 @@ psmBuildConfigs() {
         -a ci_gitCommit="${GRPC_GITREF}" \
         -a ci_gitCommit_java="${GRPC_JAVA_GITREF}" \
         -a ci_gitActualCommit="${KOKORO_GIT_COMMIT}" \
+        -a enablePrometheus=true \
         --prefix="${LOAD_TEST_PREFIX}" -u "${UNIQUE_IDENTIFIER}" -u "${pool}" -u "${proxy_type}"\
         -a pool="${pool}" \
         --category=psm \
@@ -129,6 +130,7 @@ buildConfigs() {
         -a ci_gitCommit="${GRPC_GITREF}" \
         -a ci_gitCommit_java="${GRPC_JAVA_GITREF}" \
         -a ci_gitActualCommit="${KOKORO_GIT_COMMIT}" \
+        -a enablePrometheus=true \
         --prefix="${LOAD_TEST_PREFIX}" -u "${UNIQUE_IDENTIFIER}" -u "${pool}" \
         -a pool="${pool}" --category=psm \
         --allow_client_language=c++ --allow_server_language=c++ \

tools/run_tests/performance/loadtest_examples.sh

@@ -148,6 +148,7 @@ psm_basic_example() {
         -s psm_image_prefix="\${psm_image_prefix}" \
         -s psm_image_tag="\${psm_image_tag}" \
         -s timeout_seconds=900 --prefix=psm-examples -u "${uniquifier}" -r "^${scenario}$" \
+        -a enablePrometheus=true \
         --allow_client_language=c++ --allow_server_language=c++ \
         --allow_server_language=node \
         --client_channels=8 \
@@ -178,6 +179,7 @@ psm_prebuilt_example() {
         -s psm_image_tag="\${psm_image_tag}" \
         --prefix=psm-examples -u prebuilt-"${uniquifier}" -r "^${scenario}$" \
         -a pool="\${workers_pool}" \
+        -a enablePrometheus=true \
         --allow_client_language=c++ --allow_server_language=c++ \
         --allow_server_language=node \
         --client_channels=8 \