Add an example and README for background tasks #284

Job	Run time
musl	1m 34s
Integration Tests / Test Examples/HelloWorld on 6.0.1-amazonlinux2	1m 17s
Integration Tests / Test Examples/APIGateway on 6.0.1-amazonlinux2	1m 24s
Integration Tests / Test Examples/S3_AWSSDK on 6.0.1-amazonlinux2	3m 51s
Integration Tests / Test Examples/S3_Soto on 6.0.1-amazonlinux2	4m 26s
Integration Tests / Test Examples/BackgroundTasks on 6.0.1-amazonlinux2	1m 19s
Integration Tests / Test archive plugin	2m 27s
Soundness / API breakage check	1m 41s
Soundness / Documentation check	1m 24s
Soundness / Unacceptable language check	6s
Soundness / License headers check	4s
Soundness / Broken symlinks check	4s
Soundness / Format check	47s
Soundness / Shell check	0s
Soundness / YAML lint check	10s
Soundness / Python lint check	0s
Swift 6 Language Mode / Swift 6 language mode	1m 6s
Unit tests / Unit tests / Linux (5.9)	24s
Unit tests / Unit tests / Linux (5.10)	26s
Unit tests / Unit tests / Linux (6.0)	1m 29s
Unit tests / Unit tests / Linux (nightly-6.0)	1m 49s
Unit tests / Unit tests / Linux (nightly-main)	1m 48s
Unit tests / Unit tests / Windows (6.0)	1s
Unit tests / Unit tests / Windows (nightly-6.0)	1s
Unit tests / Unit tests / Windows (nightly-main)	1s
	27m 39s

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