docs: update CIPHERS.md

Give a more consice overview of curl's cipher options and cipher suites.

Removed long lists of ciphers that were directly copied from the SSL
backends' d

docs: update CIPHERS.md

Give a more consice overview of curl's cipher options and cipher suites.

Removed long lists of ciphers that were directly copied from the SSL
backends' documentation. Instead present the user a more common aproach
acorss the SSL backends, with notes for backends that do not conform
and/or provide alternate means.

Provide a shorter list of cipher suites that is more relevant for modern
usage and should work mostly across all backends, provide a seperate
list with all cipher suites, and provide links to the SSL backends'
documentation for more information.

Also give examples with modern cipher suites.

Add docs/CIPHERS-TLS12.md for TLS 1.2 ciphers.

Closes #14460

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