Better to have all formatting on the client side, so we format the
header and the reponse values in the same place. (Also no need to
send this data over the wire as it's always the same).

PB now accommodates "lpa" and "lpr" responses as well as "af ls"

For now: puts a message in the log, does nothing and returns success.

OptionStrList takes a filename as its value. It reads the file into a
list of strings in the protobuf. On the server side, the values are
unpacked and made available as std::vector<std::string>.

For example implementation, see "cta-admin repack add"

Json output is now available by setting the XRootD debug level appropriately

Integrates XRootD logging

Not required by new SSI interface as endpoint is specified in the
workflow not in a configuration file. But it is still needed by
cta-admin.

Use in the EOS workflow/bash scripts is deprecated. However it's useful
to keep the script around for now to test the SSI workflows without needing
to invoke EOS.

Default now set to 10s. Note that XRD_TIMEOUTRESOLUTION must be set
<= 10s, otherwise timeout defaults to 15s.

Now the submodule does not provide a CMakeLists.txt file, this is now
provided by the main project (eos_cta/CMakeLists.txt)