Simple repack on CI

Usage: cta-admin --json <command> <subcommand> <options>

For stream commands only (where each line of the result is sent back in
a protocol buffer), return the results in JSON format instead of a
text table.

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).

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"

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

This allows specifying different protocol buffers for EOS and CTA Admin
messages, both of which must be processed by the same XRootD plugin in
the CTA Frontend.

Use precision .00 for Mbytes. Move library name to the front.

Converted all bytes to Mbytes. Removed extra space in the output.
Reordered fields.