Merge branch 'amiranda/19-add-a-cli-tool-for-requesting-data-transfers' into 'main'

Resolve "Add a CLI tool for requesting data transfers."

This MR adds the `ccp` tool to Cargo so that data transfers can be started
from the command line. The tool supports the following arguments:

```console
$ ccp -h
Cargo parallel copy tool
Usage: ccp [OPTIONS]

Options:
  -h,--help                   Print this help message and exit
  -s,--server ADDRESS         Address of the Cargo server (can also be
                              provided via the CCP_SERVER environment
                              variable).
  -i,--input SRC...           Input dataset(s)
  -o,--output DST...          Output dataset(s)
  --if FLAGS                  Flags for input datasets. Accepted values
                                - posix: read data using POSIX (default)
                                - mpio: read data using MPI-IO
  --of FLAGS                  Flags for output datasets. Accepted values
                                - posix: write data using POSIX (default)
                                - mpio: write data using MPI-IO
```                                

Once a Cargo server is up and running, `ccp` can be used as follows:

```console
$ srun -N4 cargo -l ofi+tcp://192.18.0.10:62000 -o cargo.log
[...]
$ ccp -s ofi+tcp://192.18.0.10:62000 -i input0.dat input1.dat -o output0.dat output1.dat
```

Modes of operation that control how transfers should be executed can be selected
through the the `--if` and `--of` options. For now, `posix` and `mpio` modes are
supported. Note however that not all combinations are supported yet, and that 
performance will depend on whether the underlying file system supports parallel
I/O through MPI-IO.

Closes #19

See merge request !13