Add documentation for druid.broker.segment.watchedTiers #24267

Job	Run time
web-checks / web-checks	21m 17s
packaging-check (21) / packaging-check-jdk21	13m 12s
packaging-check (17) / packaging-check-jdk17	12m 2s
strict-compilation / strict-compilation	20m 46s
static-checks-maven / static-checks-maven	30m 23s
openrewrite / openrewrite	15m 25s
	1h 53m 5s

Provide feedback