Provide TLS 1.3 support for 3.4.

[ramses]

What would you like to be added?

TLS 1.3 support was (re-)added to the main branch in #15156

... thus resolving #13506

However, organizations running etcd 3.4 and 3.5 are starting to require TLS 1.3 for security compliance.

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The "3.5 version" analogue issue: #15436

Why is this needed?

As stated above, organizations running etcd 3.4 and 3.5 are starting to require TLS 1.3 for security compliance. Also, waiting for etcd 3.6 is not compatible with their timelines.

[ahrtr]

Makes sense to me. Please feel free to deliver a PR, thx

[jmhbnz]

Initial backport pr open #15486 and docs pr open here etcd-io/website#650. I will raise pr for changelog shortly.

/assign
/remove help