builtin/multi-pack-index.c: make '--progress' a common option

builtin/multi-pack-index.c: make '--progress' a common option

All multi-pack-index sub-commands (write, verify, repack, and expire)
support a '--progress' command-line option, despite not listing it as
one of the common options in `common_opts`.

As a result each sub-command declares its own `OPT_BIT()` for a
"--progress" command-line option. Centralize this within the
`common_opts` to avoid re-declaring it in each sub-command.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>