install.sh: create a www_fullchain.pem file
Apache has a "unique" configuration setup where the server's leaf
certificate is configured by the `SSLCertificateFile` directive
but the rest of the server's certificate chain is set using the
`SSLCertificateChainFile` directive.
Other server software just has a single directive that specifies
a file that starts with the server's leaf and may also contain
the rest of the certificate chain in order in that same file.
Create a ..._www_fullchain.pem file that contains this full
certificate chain during installation in case it might be needed
by non-Apache server software.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>