bug: MemoryManager uses CN memory allocation for total_memory

[fuyufjh]

Here we assumed that the total memory of CN is only used for 3 portions: compute, storage and reserve.

risingwave/src/compute/src/server.rs

Lines 291 to 299 in 67bdcd7

	// NOTE: Due to some limits, we use `compute_memory_bytes + storage_memory_bytes` as
	// `total_compute_memory_bytes` for memory control. This is just a workaround for some
	// memory control issues and should be modified as soon as we figure out a better solution.
	//
	// Related issues:
	// - https://github.com/risingwavelabs/risingwave/issues/8696
	// - https://github.com/risingwavelabs/risingwave/issues/8822
	let memory_mgr = MemoryManager::new(MemoryManagerConfig {
	total_memory: compute_memory_bytes + storage_memory_bytes,

However, the standalone node breaks this assumption. This will cause the MemoryManager to use less memory than expected.