Guard the mode configs map in GamePackageConfiguration with lock

Synchronizes the getter and setter of GameModeConfiguration as the sub
fields can be read/write by different callers

Bug: b/240335717
Test: atest GameManagerServiceTests
Change-Id: Iac718a6a5d91e7aa3452b5cdb9aaee587f6f7773
Merged-In: Iac718a6a5d91e7aa3452b5cdb9aaee587f6f7773