dumpstate.cpp: increase perfetto serialization timeout

This commit increases the timeout of "perfetto --save-for-bugreport"
from 10s to 30s, thus giving more time to data sources to process
OnFlush.

30s seems a bit extreme but in production we ran into cases
(e.g. b/369053554), where the serialization took >18s.

Fix: 369053554
Flag: EXEMPT bugfix
Test: atest com.android.os.bugreports.tests.BugreportManagerTest
Ignore-AOSP-First: depends on changes not available in AOSP
       (I343813929a537c601132dd15db5e2c4d3fbbdcb1)
Change-Id: Ie976c7d86fef854f24b115b347890a3d40be9885