App support when using Apptainer containers

[thealanjason]

In case we want to a single container with different apps in different nextflow processes(computational units), this is possible.

All we need to do is:

1. Use the env( NXF_APPTAINER_RUN_COMMAND ) as an input to the process and provide the input as run, to use the apptainer run command instead of apptainer exec
2. In the process, provide the app name through the containerOptions directive. For example containerOptions "--app <app_name>"