Add ML benchmark for imaging calorimetry

benchmarks/imaging_shower_ML/config.yml

 ml_shower:tagging_epi :
   extends: .rec_benchmark
   when: manual
-  stage: process
+  stage: benchmark1
   timeout: 8 hour
   script:
     - python3 benchmarks/imaging_shower_ML/sim_rec_tag.py -t imshower -n 10000 --particles "electron,pion-,pion-" --pmin 0.5 --pmax 10
@@ -10,7 +10,7 @@ ml_shower:tagging_epi :
 ml_shower:tagging_e :
   extends: .rec_benchmark
   when: manual
-  stage: process
+  stage: benchmark1
   timeout: 8 hour
   script:
     - python3 benchmarks/imaging_shower_ML/sim_rec_tag.py -t imshower -n 10000 --particles "electron" --pmin 0.5 --pmax 10
@@ -18,7 +18,7 @@ ml_shower:tagging_e :
 ml_shower:tagging_pi :
   extends: .rec_benchmark
   when: manual
-  stage: process
+  stage: benchmark1
   timeout: 8 hour
   script:
     - python3 benchmarks/imaging_shower_ML/sim_rec_tag.py -t imshower -n 10000 --particles "pion-" --pmin 0.5 --pmax 10