doc: add a reference to the list of OpenSSL flags.
Some of the SSL_OP_* constants are missing description in the documentation. Instead of rewriting the description from OpenSSL's wiki, I have decided to put a link to a detailed list in the 'OpenSSL Options' section.
I see no point of doing both - adding a reference to the wiki and adding constant descriptions - but I might do if presented with convincing arguments.
This is a follow-up to #33929.
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documentation is changed or added -
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