docs: update CIPHERS.md

[jan2000]

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.

[jan2000]

So I have added this TLS 1.2 ciphers list document, that serves as a reference for the updated CIPHERS.md doc. But I am not to sure about the location of this document. For now I put it in docs/CIPHERS-TLS12-ALL.md, but there it obviously fails the CI spell checker. Any suggestions?

[bagder]

I propose you drop ALL from the filename and make it: docs/CIPHERS-TLS12.md

Then I think we can skip this file in the spellcheck CI job:

--- a/.github/scripts/spellcheck.yaml
+++ b/.github/scripts/spellcheck.yaml
@@ -27,6 +27,6 @@ matrix:
             - 'code'
             - 'pre'
             - 'strong'
             - 'em'
     sources:
-      - '**/*.md|!docs/BINDINGS.md|!docs/DISTROS.md'
+      - '**/*.md|!docs/BINDINGS.md|!docs/DISTROS.md|!docs/CIPHERS-TLS12.md'

[bagder]

Thanks!