Absolute SSL path should work for postgres recipe

• Users who set an absolute file path for their postgres SSL certificate will see gitlab-ctl reconfigure fail because the addition of Patroni in commit 5c1d80c2 changed to using File.join for building the path versus File.absolute_path
• Adds tests to ensure that if a user sets ssl_cert_file or ssl_key_file to an absolute path that it will retain the behavior of using that exact path

Closes #5463 (closed)

Signed-off-by: Robert Marshall rmarshall@gitlab.com