Update gh-workflow to trigger only on specific events (#7740)

Signed-off-by: NHrishikesh Barman <hrishikeshbman@gmail.com>

.github/workflows/funcbench.yml

 on: repository_dispatch
+  repository_dispatch:
+    types: [funcbench_start]
 name: Funcbench Workflow
 jobs:
   run_funcbench:

.github/workflows/prombench.yml

 on: repository_dispatch
+  repository_dispatch:
+    types: [prombench_start,prombench_restart,prombench_stop]
 name: Prombench Workflow
 env:
   AUTH_FILE: ${{ secrets.TEST_INFRA_GKE_AUTH }}