Add some documentation of the CAS cleanup functionality

This documents how the cleanup tool should be used, and describes some
of the tradeoffs involved in its configuration.
7 jobs for sotk/indexed-cas/documentation in 21 minutes and 20 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #593021367
cleanup-compose-test

00:07:21

passed #593021370
documentation

00:10:03

passed #593021360
dummy-tests

00:09:32

passed #593021363
e2e-tests

00:14:00

passed #593021358
type-check

00:10:02

passed #593021356
unit-tests

00:19:46

 
  Post
passed #593021372
coverage

00:01:34

83.24%