text: Title: Add option to customise names of grid tasks.
  Body: When running tasks in a grid, a number is appended at the end of the tasks product names. For example, the following pipeline.yaml file:
  
  ```
  - source: example_task.py
     name: example-task
     product:
         data: output/output_dataframe.csv
     grid:
         input_dataframe: ['birds.csv', 'fish.csv', 'flowers.csv']
  ```
  
  would result in 3 products: output_dataframe-1.csv, output_dataframe-2.csv and output_dataframe-3.csv.
  
  I would like to have an option to replace -1, -2 and -3 in the filenames with for example -birds, -fish and -flowers.