Add settings for KernelCpuThreadReader

Settings include:
- Number of buckets
- UID predicate for which threads to collect data for

Test: to test UID selection: `atest KernelCpuThreadReaderTest`
Test: to test settings application: `adb shell cmd settings put ...` and
manual inspection of `pull-source`
Bug: 123562450
Change-Id: I9d97dfc1c120fcf1b04dadb6ce24863afeff053c