Improve config compiler performance.

Refs #5327
Avoid using ConfigItem::GetObject when possible.

Refs #5327
Implement ParallelWorkQueue class.

Refs #5327
Improve WorkQueue performance

Refs #5327
Improve performance for icinga::Deserialize.

Refs #5327
Merge branch 'feature/tp-contention-5327' into next

Fixes #5327