Add an example and README for background tasks #286

Job	Run time
musl	1m 40s
Integration Tests / Test Examples/HelloWorld on 6.0.1-amazonlinux2	1m 17s
Integration Tests / Test Examples/APIGateway on 6.0.1-amazonlinux2	1m 16s
Integration Tests / Test Examples/S3_AWSSDK on 6.0.1-amazonlinux2	3m 53s
Integration Tests / Test Examples/S3_Soto on 6.0.1-amazonlinux2	4m 37s
Integration Tests / Test Examples/BackgroundTasks on 6.0.1-amazonlinux2	1m 14s
Integration Tests / Test archive plugin	2m 33s
Soundness / API breakage check	1m 44s
Soundness / Broken symlinks check	3s
Soundness / License headers check	5s
Soundness / Unacceptable language check	6s
Soundness / Documentation check	1m 30s
Soundness / Format check	39s
Soundness / Python lint check	0s
Soundness / Shell check	0s
Soundness / YAML lint check	3s
Swift 6 Language Mode / Swift 6 language mode	1m 14s
Unit tests / Unit tests / Linux (5.9)	26s
Unit tests / Unit tests / Linux (5.10)	26s
Unit tests / Unit tests / Linux (6.0)	1m 28s
Unit tests / Unit tests / Windows (6.0)	4s
Unit tests / Unit tests / Linux (nightly-6.0)	1m 44s
Unit tests / Unit tests / Linux (nightly-main)	1m 52s
Unit tests / Unit tests / Windows (nightly-6.0)	3s
Unit tests / Unit tests / Windows (nightly-main)	4s
	28m 1s

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