Change date release candidate is cut

[lukeheath]

I want to try cutting the release candidate on the first day of each sprint.

Since moving to the release train model, it's created a situation where the last week of every sprint is work going towards the next release, not the current release.

This change will have the following benefits:

1. The business will be able to more accurately forecast what will be delivered each sprint.
2. The work produced during the sprint will ship sooner and provide value to our customers sooner.
3. From the first day to the last day of each sprint, work can be merged into main, and all of that work will ship with the next release.

The cost I see are:

1. QA won't be fully smoke testing the release until the next sprint kicks off, which means engineers will get called back for unreleased bugs.

But, this is happening already, because the last week of the sprint the engineers are shifting to next release.