Ubiquiti removed keytool (and java) from recent releases of Unifi OS. This moves from keytool to openssl's native pkcs12.
Tested on Unifi Dream Machine which runs Unifi OS and a built-in Unifi controller.
Also added backup of existing files prior to change in case anything goes wrong, and update system configuration with compatible ciphers.
When there are errors with namecheap hosts, acme.sh fails with:
dns_namecheap.sh: line 262: _error: command not found
Based on usage elsewhere in the file, I believe this should be _err