Folds in #4853: hive-c0re no longer writes branch protection on
`agent-configs` repos (apply_config_repo_branch_protection,
config_repo_protection_edit, record_branch_protection_result and the
now-unused main_branch_protection_option go). swarm-controller's
CreateRepo rule and its forge-objects convergence own `main`'s gate.
Nothing merges into config `main` as `core` any more, so the converged
rule's merge user list is empty. `push_config` still pushes `main` as
core, through push rights, not the merge whitelist.
Refs #4850
Refs #4853
0cee0382e9