Add feature flag configuration for every build type

[wmontwe]

In #8786 we documented the new release train model.

To satisfy the feature flag rules we have to ensure that:

• On main, feature flags are enabled as soon as developers have completed all pull requests related to the feature.
• On beta, feature flags remain enabled unless the feature has not been fully completed and the developers would like to pause the feature.
• On release, feature flags are disabled until an explicit decision has been made to enable the feature for all users.

This requires us to provide a feature flag configuration for every build type to allow different configurations.