Initial conversion to textproto

Convert trunk_staging to textproto.

This change produces no effective difference in the generated release
config.

Bug: 328495189
Test: manual
Merged-In: I8ccfdaf55f7672421584f0bcd012f7f48563718d
Change-Id: Iee0a7211281d391c7f618f0238e8c1e72f7211a8