Also:
- Rename to use FRESHCLAM_CLIENT_CERT, FRESHCLAM_CLIENT_KEY instead
prefixing with "CURL_". Unlike CURL_CA_BUNDLE, these variable names
are not used by the `curl` program and so do not piggyback on that
existing functionality.
- Add FRESHCLAM_CLIENT_KEY_PASSWD environment variable to support
password protected private key PEM files, as described in:
https://curl.se/libcurl/c/CURLOPT_SSLCERT.html
- Document the new environment variable options in the manpage and in
the `freshclam --help` message. Also add missing documentation in the
freshclam and clamsubmit help-messages for CURL_CA_BUNDLE.
- Update the NEWS.md file to credit jedrzej for the new feature.
The named "shared" is confusing, especially now that these features are
built as a static library instead of being directly compiled into the
various applications.
