Release pipeline - conditionalize and parameterize backport check

The backport check in the release pipeline should be one that is executed if and only if toggled as a build parameter, similar to Dry Run. For example, during the release of 1.9.0.Alpha1, there is no reason to run this task; this task should only be enabled for when doing older releases, such as 1.8.1.Final.

In addition to it being conditionalized, the build process should either pass in via build parameters or via some pipeline logic the parameters needed for the script. As of now the script is executed without such parameters and fails.