Provide a way for CI pipeline to test CRI_XCBC PRs

Currently, there is no way to test the PRs submitted from the forks of jprorama/CRI_XCBC repo to jprorama/CRI_XCBC because we hardcoded the upstream and downstream repos and their branch names in the ci pipeline script. We need to be able to specify them as variables so that their values can be defined according to the developer requirements during the dev pipeline runs. This will enable a developer to define the branch names of the PRs they want to test from the repos they want.