Make inclusion of Nextflow log in runs dump output optional

[ejseqera]

Related to seqeralabs/nf-aggregate#70, it would be helpful to make the inclusion of the Nextflow log file in the runs dump archive optional so a user can still pull the details of a run, even after the work directory of the run has been deleted in object storage without the CLI throwing an error or causing other programs to terminate.

For example, similar to the task logs, adding a --add-nextflow-log option to the tw runs dump command or this functionality could be captured with a modified --add-logs flag:

Usage: tw runs dump [OPTIONS]

Dump all logs and details of a run into a compressed tarball file for troubleshooting.

Options:
* -i, -id=<id>                  Pipeline run identifier.
* -o, --output=<outputFile>     Output file to store the dump. (supported formats: .tar.xz and .tar.gz)
      --add-task-logs           Add all task stdout, stderr and log files.
      --add-fusion-logs         Add all Fusion task logs.
      --add-nextflow-log        Add Nextflow log file.
      --only-failed             Dump only failed tasks.
      --silent                  Do not show download progress.
  -w, --workspace=<workspace>   Workspace numeric identifier (TOWER_WORKSPACE_ID as default) or workspace reference as OrganizationName/WorkspaceName
  -h, --help                    Show this help message and exit.
  -V, --version                 Print version information and exit.