Add CpuMonitorService to monitor CPU stats.

- This service will be published as a local system server service.
- Other system server services such as job scheduler can use this
  service to monitor CPU availability.
- Support for reading Kernel sysfs and procfs files and monitoring the
  CPU availability will be added in the following CLs.

Test: atest CpuMonitorServiceTest
Bug: 242722241
Change-Id: Ia2565a67a5f639a8d5975d42b0b84d95d08e099f