Change behaviour of prediction mode

[peter-t-fox]

• [x] Add ability to run multiple iterations of the selected model in prediction mode, controlled by an input parameter
• [x] Alter format of "full" file to have one row per iteration, day, age group. Add header row.
• [x] Remove "ends" file as it duplicates the content of the "full" file.

[github-actions[bot]]

Heads up @thibaud-porphyre @peter-t-fox - the "Covid19_EERAModel" label was applied to this issue.