Add repack.repack_buffer_url in a cta-admin command

Problem to solve

Currently repack.repack_buffer_url is only available in cta-admin --json re ls command.

The problem is that this information is not available if there is no tape being currently repacked.

This information is needed from the tape servers to perform the tape-extract operation on pathologic tapes data recovery.

In this case the repack requests must be deleted before data extraction as we have no way to stop the repack operations: the tape is already disabled and repack ignores the disabled state.

Intended users

Tape operators launching tape-extract on a broken tape.

Proposal

Could this information be added to a cta-admin command so that it is available outside of repack requests?

Currently the closest command is cta-admin version as this command reports cta-frontend properties/configuration.

This is a --json only field that should not be exposed in the standard output.