docs: documentation and sample for grpc endpoints #384

Job	Run time
Basic checks	50s
Build and publish artifacts and plugins locally	1m 32s
Run annotation processor tests	1m 11s
Check service docker image contents	38s
Run sbt test	1m 48s
Maven samples (shopping-cart-quickstart, true)	39s
Maven samples (grpc-shopping-cart-quickstart, true)	1m 13s
Maven samples (choreography-saga-quickstart, true)	49s
Maven samples (doc-snippets, false)	45s
Maven samples (view-store, true)	1m 17s
Maven samples (spring-dependency-injection, true)	43s
Maven samples (event-sourced-customer-registry, true)	1m 3s
Maven samples (event-sourced-counter-brokers, docker compose up -d, true)	1m 41s
Maven samples (event-sourced-customer-registry-subscriber, true, ./start-upstream.sh)	1m 5s
Maven samples (key-value-counter, true)	39s
Maven samples (key-value-shopping-cart, true)	54s
Maven samples (key-value-customer-registry, true)	1m 9s
Maven samples (tracing, false)	27s
Maven samples (reliable-timers, true)	42s
Maven samples (transfer-workflow, true)	48s
Maven samples (transfer-workflow-compensation, true)	50s
	20m 43s

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