make BufferedLogService thread safe

[StevenMassaro]

Impact

• Bug fix (non-breaking change which fixes expected existing functionality)
• Enhancement/New feature (adds functionality without impacting existing logic)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

Makes the underlying log store for the BufferedLogService thread safe.

Things to be aware of

We occasionally get errors like:

java.util.ConcurrentModificationException
	at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1043)
	at java.base/java.util.ArrayList$Itr.next(ArrayList.java:997)
	at liquibase.logging.core.BufferedLogService.getLogAsString(BufferedLogService.java:39)
	at ...

in the pro integration tests, this should resolve them.

Things to worry about

Performance impacts from the synchronized list? This is unlikely because Liquibase is not a terribly thread-heavy application.

Additional Context

[github-actions]

Unit Test Results

  4 740 files  ±0    4 740 suites  ±0   35m 25s ⏱️ -44s
  4 693 tests ±0    4 457 ✔️ ±0     236 💤 ±0  0 ❌ ±0 
55 536 runs  ±0  50 228 ✔️ ±0  5 308 💤 ±0  0 ❌ ±0 

Results for commit 5a91345. ± Comparison against base commit 0aa4be9.

♻️ This comment has been updated with latest results.

[filipelautert]

JVM must be smart enough that performance impact in single thread environments may be 0.