refactor: log when using a preconfig git source. (#416)
refactor: log when using a preconfig git source. (#416)

Co-authored-by: Jeff Ching <21aaffda9718a203d3f6dfde95bf7c5668b929a6@google.com>

googleapis/synthtool,googleapis/synthtool,googleapis/synthtool,googleapis/synthtool,googleapis/synthtool