featureflag: Enable first batch of transactional RPCs
Enable transactional behaviour for the first batch of RPCs. The toggled RPCs have all been enabled in production either since January 27th or since February 1st.
Relates to gitlab-com/gl-infra/production#3706 (closed) and gitlab-com/gl-infra/production#3444 (closed).
Part of #3310 (closed)