Add option to move files from polling directory instead of delete

[skliper]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I reviewed the CF README.md file to see if the feature is in the major future work.
• I performed a cursory search to see if the feature request is relevant, not redundant, nor in conflict with other tickets.

Is your feature request related to a problem? Please describe.
Only way to send a file without deleting is by command which unnecessarily limits design options.

Intra-app commands isn't ideal, but currently the only option if you want to automate sending files without deleting them. Also nicer for automated data prioritization algorithms to query the number of files in the polling directory (assuming just file count resolution is needed), vs more complex methods of tracking how much data is actually queued via the individual commands, processing CF tlm or similar.

Describe the solution you'd like
Support moving the file from the polling directory instead of always deleting. Possibly rework the keep option to support a move if the move directory is defined (via config) and available. Also useful for commanded cases to just move when done.

Describe alternatives you've considered
None

Additional context
None

Requester Info
Jacob Hageman - NASA/GSFC

[skliper]

Might help to also have a delete on move fail or keep on move fail option. For the polling directory you'd likely always want to delete, but for a commanded send keeping the file on move fail seems like a valid use case.