[FEATURE] Multiple choice

**Is your feature request related to a problem? Please describe.**
Be able to select multiple choices

**Describe the solution you'd like**
An checkbox option in the configuration to set the select input as singular or multiple choice

**Describe alternatives you've considered**
Multiple input parameters all pointing to the same webservice but very impractical

**Additional context**
None

No files or tests are named in the issue. Start by locating the configuration and select-input handling for the REST-backed parameter, then trace how the current singular choice is represented. Done means configuration can choose singular or multiple selection and multiple selected values are sent to the web service correctly.

Written by the indexing model from the issue text.