[Feature Proposal] Handle existing chain.pem during import about unifi-docker

[jacobalberty]

Easy enough to add the CERTNAME part, just use something like
CERTNAME="${CERTNAME:-cert.pem}" to the top then replace the rest of the references to cert.pem with ${CERTNAME}

as far as the CHAINPROVIDED bit it's easy enough to add an if statement just need to be sure the TMPLIST stuff doesn't get too buggered and end up leaving a bunch of temp files every time the cert changes.

There is one other change that needs to be accounted for if you want filenames to be changed modified easily. The privkey.pem will still be hardcoded.

[ffittschen]

I just created a PR as you can see. I went with an IMO clearer name CERT_IS_CHAIN instead of CHAINPROVIDED. I hope this is ok