[core] (cgroups 16/n) Changing the algorithm for default values for system reserved resources

[israbbani]

This PR stacks on #57269 .

For more details about the resource isolation project see #54703.

In this PR, I've revised the algorithm for choosing default values for system-reserved-cpu and system-reserved-memory. The intent behind the algorithm is to:

1. pick the value as a proportion of the available system resources where the proportion is specified by DEFAULT_SYSTEM_RESERVED_{MEMORY|CPU_CORES}_PROPORTION
2. if the value < DEFAULT_MIN_SYSTEM_RESERVED_{CPU_CORES|MEMORY}, use the constant.
3. if the value > DEFAULT_MAX_SYSTEM_RESERVED_{CPU_CORES|MEMORY}, use the constant.

This has a few useful properties

• on small machines, there's a minimum value (avoiding pathological cases like 5% of 1 core is 0.05 cores reserved for the system cgroup)
• for larger machines, the value scales up with the amount of available resources up to a maximum (avoiding pathological cases like on a 128 core machine, 6 cores are reserved for system processes)

[edoakes]

@israbbani I merged upstream and re-triggered CI after merging the other one; ping to merge if tests pass here