docs: documentation and sample for grpc endpoints #386

Job	Run time
Basic checks	48s
Build and publish artifacts and plugins locally	1m 35s
Run sbt test	2m 53s
Check service docker image contents	42s
Run annotation processor tests	1m 0s
Maven samples (shopping-cart-quickstart, true)	39s
Maven samples (grpc-shopping-cart-quickstart, true)	1m 7s
Maven samples (choreography-saga-quickstart, true)	52s
Maven samples (doc-snippets, false)	49s
Maven samples (view-store, true)	1m 25s
Maven samples (spring-dependency-injection, true)	43s
Maven samples (event-sourced-customer-registry, true)	1m 19s
Maven samples (event-sourced-counter-brokers, docker compose up -d, true)	1m 46s
Maven samples (event-sourced-customer-registry-subscriber, true, ./start-upstream.sh)	1m 23s
Maven samples (key-value-counter, true)	47s
Maven samples (key-value-shopping-cart, true)	49s
Maven samples (key-value-customer-registry, true)	51s
Maven samples (tracing, false)	28s
Maven samples (reliable-timers, true)	38s
Maven samples (transfer-workflow, true)	37s
Maven samples (transfer-workflow-compensation, true)	59s
	22m 10s

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