Enhance verify(1) to output the constructed chain certificates, not just the subject names as with `-short_chain`.

Presently, there is not a natural way to take a certificate and output its full trust path to an anchor in the trust store.

Also given a PEM file with certs, there isn't a natural way to output the text form of each certificate along with optoinally the PEM blobs.

Currently we have:

# Dump the text of multiple certs, far from obvious
$ openssl crl2pkcs7 -nocrl -certfile foo.pem | openssl pkcs7 -print_certs -text

# Construct a trust path:
$ openssl pkcs12 -export -chain -nokeys -passout pass:whatever \
       -in cert.pem -untrusted chain.pem |
       openssl pkcs12 -in /dev/stdin -passin pass:whatever

Ideally the 2nd use-cases should be possible with verify(1), while the first could be a "-multi" or similar option in x509(1).

### Tasks
- [ ] develop documentation for new option
- [ ] implement new option in verify command to output full cert chain in PEM format
- [ ] Add CI test to validate new option

Start with the verify(1) command and its existing -short_chain behavior, then review how x509(1) handles certificate output and how CI tests are organized. Define the new option's full-chain PEM output from the task description, add documentation and a CI test, and consider the separate x509(1) multi-certificate use case.