Keeping the old release requires using the https://zlib.net/fossils/ base URL

Ticket: ENT-9517
Changelog: none

…l pull/push usage

Before I was pulling the sftp cache on the host outside the container because
I couldn't figure out how to push the sftp cache private key inside the container.

When I changed a dependency, zlib in this case, the build scripts wanted to push
the new packages up to the sftp cache which failed due to lack of private key in the container.

This commit takes either a github secret or mystiko password and sets it as an environment variable inside the container for the build to use.

Ticket: ENT-10419
Changelog: none