remote: add camel-cased *.tagOpt key, like clone

remote: add camel-cased *.tagOpt key, like clone

Change "git remote add" so that it adds a *.tagOpt key, and not the
lower-cased *.tagopt on "git remote add --no-tags", just as "git clone
--no-tags" would do.

This doesn't matter for anything that reads the config. It's just
prettier if we write config keys in their documented camelCase form to
user-readable config files.

When I added support for "clone -no-tags" in 0dab2468ee5 (clone: add a
--no-tags option to clone without tags, 2017-04-26) I made it use
the *.tagOpt form, but the older "git remote add" added in
111fb858654 (remote add: add a --[no-]tags option, 2010-04-20) has
been using *.tagopt all this time.

It's easy enough to add a test for this, so let's do that. We can't
use "git config -l" there, because it'll normalize the keys to their
lower-cased form. Let's add the test for "git clone" too for good
measure, not just to the "git remote" codepath we're fixing.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>