如何将 Let's Encrypt 的 RSA 4096 位替换为 ECC 256 位?

@mpalmer does this request make sense to you? Is there anything off with our current certificate config in NGINX?

OK per https://www.ssl247.com/kb/ssl-certificates/generalinformation/what-is-rsa-dsa-ecc ECC is latest and greatest, so I guess we should at least document how to do this. Not sure.