Re: [PATCH v3 4/5] fetch: respect --server-option when fetching multiple remotes

"Xing Xin via GitGitGadget" [off-list ref] writes:

From: Xing Xin <redacted>

Fix an issue where server options specified via the command line
(`--server-option` or `-o`) were not sent when fetching from multiple
remotes using Git protocol v2.

To reproduce the issue with a repository containing multiple remotes:

  GIT_TRACE_PACKET=1 git -c protocol.version=2 fetch --server-option=demo --all

Observe that no server options are sent to any remote.

The root cause was identified in `builtin/fetch.c:fetch_multiple`, which
is invoked when fetching from more than one remote. This function forks
a `git-fetch` subprocess for each remote but did not include the
specified server options in the subprocess arguments.

This commit ensures that command-line specified server options are
properly passed to each subprocess. Relevant tests have been added.

A more interesting use case, as there is no reason to expect that a
single server-option command line option may apply to all remotes,
would be to configure different server options for different remotes
via the new serverOption configuration, so that different server
options are used for different remotes.

If it happens that the same server option is applicable for all
remotes, it is reasonable to give --server-option from the command
line and expect it to be propagated down to subfetches, so
regardless of the "what happens when different remotes have
different options configured?" above, the change in this step looks
reasonable to me.