fetch: add --negotiation-include option for negotiation

fetch: add --negotiation-include option for negotiation

Add a new --negotiation-include option to 'git fetch', which ensures
that certain ref tips are always sent as 'have' lines during fetch
negotiation, regardless of what the negotiation algorithm selects.

This is useful when the repository has a large number of references, so
the normal negotiation algorithm truncates the list. This is especially
important in repositories with long parallel commit histories. For
example, a repo could have a 'dev' branch for development and a
'release' branch for released versions. If the 'dev' branch isn't
selected for negotiation, then it's not a big deal because there are
many in-progress development branches with a shared history. However, if
'release' is not selected for negotiation, then the server may think
that this is the first time the client has asked for that reference,
causing a full download of its parallel commit history (and any extra
data that may be unique to that branch). This is based on a real example
where certain fetches would grow to 60+ GB when a release branch
updated.

This option is a complement to --negotiation-restrict, which reduces the
negotiation ref set to a specific list. In the earlier example, using
--negotiation-restrict to focus the negotiation to 'dev' and 'release'
would avoid those problematic downloads, but would still not allow
advertising potentially-relevant user branches. In this way, the
'include' version solves the problem I mention while allowing
negotiation to pick other references opportunistically. The two options
can also be combined to allow the best of both worlds.

The argument may be an exact ref name or a glob pattern. Non-existent
refs are silently ignored. This behavior is also updated in the ref matching
logic for the related --negotiation-restrict option to match.

The implementation outputs the requested objects as haves before the
negotiator performs its own algorithm to choose the next haves. Use the new
have_sent() interface to signal these have commits were sent before engaging
with the negotiator's next() iterator.

Also add --negotiation-include to 'git pull' passthrough options.

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>