Add support for proxy types CURLPROXY_HTTPS and CURLPROXY_HTTPS2

[vog]

Add support for proxy types CURLPROXY_HTTPS and CURLPROXY_HTTPS2.

Also, fix order of variants to be consistent with the libcurl documentation, and provide complete availability information.

See also:

• https://curl.se/libcurl/c/CURLOPT_PROXYTYPE.html
• https://github.com/curl/curl/blob/e5087ac9fc6c80fbb1708b750e8187c7c876f0a4/include/curl/curl.h#L790-L804

[nojb]

This increases to minimum required libcurl version to 8.1.0 (May 17 2023).

ocurl goes to considerable lengths to support old versions of libcurl. Can you try to implement the new feature without changing the minimum version? You can look around curl-helper.c for inspiration.

[vog]

This increases to minimum required libcurl version to 8.1.0 (May 17 2023).

ocurl goes to considerable lengths to support old versions of libcurl. Can you try to implement the new feature without changing the minimum version? You can look around curl-helper.c for inspiration.

Thanks for the hint. I just fixed that. Please review again.

[vog]

@nojb I just pushed an improved version based on your feedback. Please review once again. Thank you so far for your timely feedback! 👍

[nojb]

LGTM

[nojb]

Merged, thanks.