https://github.com/acmesh-official/acme.sh/wiki/Preferred-Chain
2. clear some code.
--list
2. get EAB credentials from Zerossl by email automatically
--server
2. Support Zerossl.com acme protocol. 3. Add "--set-default-ca --server xxxx" command to set the default CA to use.
https://github.com/acmesh-official/acme.sh/issues/2939#issuecomment-632481658
https://github.com/acmesh-official/acme.sh/issues/2939
https://github.com/acmesh-official/acme.sh/issues/2856
fix https://github.com/acmesh-official/acme.sh/issues/2833
fix https://github.com/acmesh-official/acme.sh/issues/2773
fix https://github.com/acmesh-official/acme.sh/issues/2768