This ticket has two parts:

• Create a new MigratingTenantAccessBlockerByPrefix class that is a decoration on ServiceContext (see example). The class should go in a new migrating_tenant_access_blocker_by_prefix{.h, .cpp} file and be linked in to the serveronly_repl library. The class should contain a StringMap from database prefix to shared_ptr<MigratingTenantAccessBlocker> and have a member mutex to synchronize access to the StringMap (see example). The class should have the following methods:
  • add(StringData dbPrefix, shared_ptr<MigratingTenantAccessBlocker> mtab)
  • remove(StringData dbPrefix)
  • shared_ptr<MigratingTenantAccessBlocker> get(StringData dbName)
  • void appendInfoForServerStatus(BSONObjBuilder* builder).
• Add a ServerStatusSection for the MigratingTenantAccessBlockerByPrefix class in a new migrating_tenant_access_blocker_server_status_section.cpp file that is linked in to the serveronly_repl library. The ServerStatusSection::generateSection should call MigratingTenantAccessBlockerByPrefix::appendInfoForServerStatus (see example). The actual serverStatus output may change a bit, but for now let's just expose the state in each MigratingTenantAccessBlocker by adding a MigratingTenantAccessBlocker::appendInfoForServerStatus that appends the '_access' variable, _blockTimestamp (if set) and _commitOrAbortOpTime (if set).

Manually test that the info about MigratingTenantAccessBlockerByPrefix appears in serverStatus output. You can do this by calling MigratingTenantAccessBlockerByPrefix::add somewhere in mongod startup, e.g. here.