Improve experience when `dualPublish` is configured

[erichaagdev]

The following 2 problems exist when dualPublish is configured:

• If the secondary publish succeeds, its build scan is written to the build-scans.csv file and its build scans are used to create the summary
• If the secondary publish fails but the primary publish succeeds, the experiment aborts (see below)

We should consider making the following changes:

• If the secondary publish succeeds, do not write its contents to build-scans.csv and always use the build scans from the primary publish to create the summary
• If the secondary publish fails but the primary publish succeeds, do not abort the experiment and continue

We need to confirm that the callbacks from the primary publish will always complete before the callbacks of the dualPublish.