documentation: send-email: use camel case consistently

documentation: send-email: use camel case consistently

Correct a few random "sendemail.*" configuration parameter names in the
documentation that, for some unknown reason and contrary to the expected,
didn't use camel case format.

The majority of the corrections are straightforward, by using camel case
to denote boundaries of the individual words that, stringed together, make
up configuration parameter names.  A couple of abbreviations found in some
of the corrected configuration parameter names present some exceptions,
which are described in detail below.

First, there's "SSL" as the abbreviation for "Secure Sockets Layer". [1]
As such, it's written using all uppercase letters, which is pretty much the
general rule for making abbreviations, although with certain exceptions.

Second, there's "Cc" as the abbreviation for "carbon copy", which is another
exception.  As the acronym for "carbon copy", "cc" (mind the all lowercase
letters) stems from the rather old times when, literally, carbon copies were
made. [2]  Therefore, using "CC" (mind the all uppercase letters) or "cc"
(mind the all lowercase letters) would be technically correct in the email
domain, as the abbreviation or as mentioned in RFC2076, [3] respectively, but
the age of email has established "Cc" (mind the mixed uppercase and lowercase
letters) as some kind of de facto standard. [1][4][5]  Moreover, some of the
git utilities, primarily git-send-email(1), already refer to making email
carbon copies as specifying "Cc:" email headers.  As a result, "Cc" becomes
one of the exceptions to the general rule for making abbreviations.

[1] https://en.wikipedia.org/wiki/Transport_Layer_Security
[2] https://en.wikipedia.org/wiki/Carbon_copy
[3] https://datatracker.ietf.org/doc/html/rfc2076
[4] https://bugzilla.mozilla.org/show_bug.cgi?id=212059
[5] https://bugzilla.mozilla.org/show_bug.cgi?id=50826

Signed-off-by: Dragan Simic <dsimic@manjaro.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>