This change increases the maximum memory usage for index builds during initial sync to 10% of available RAM by default, at least 200MB, and up to 16GB. These thresholds can be tuned with the following setParameters: initialSyncIndexBuildMemoryPercentage, initialSyncIndexBuildMemoryMinMB, and initialSyncIndexBuildMemoryMaxMB.

SERVER-102428 effectively reduces the memory allocated to the simultaneous index builds during initial sync. We should give initial sync a larger amount of memory to build indexes. There's no reason why it needs to obey the index build default memory limits.