remote: add remote.*.negotiationRestrict config

remote: add remote.*.negotiationRestrict config

In a previous change, the --negotiation-restrict command-line option of 'git
fetch' was added as a synonym of --negotiation-tip. Both of these options
restrict the set of 'haves' the client can send as part of negotiation.

This was previously not available via a configuration option. Add a new
'remote.<name>.negotiationRestrict' multi-valued config option that updates
'git fetch <name>' to use these restrictions by default.

If the user provides even one --negotiation-restrict argument, then the
config is ignored.

An empty value resets the value list to allow ignoring earlier config
values, such as those that might be set in system or global config.

Reviewed-by: Matthew John Cheetham <mjcheetham@outlook.com>
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>