Automatically sync private feature repo with main repo

[sichanyoo]

Background

In build system, if private feature repo gets too out of date against the main repo, it fails to find the branching point between the two repos as it only fetches a limited number of past commits. This fails the E2E test as it fails to merge the code from customization repo into the main repo.

Task

• Make private feature repo automatically sync with main repo at regular intervals
• Enable disabled E2E test on build system that tests customizations.