docs: documentation and sample for grpc endpoints #392

Job	Run time
Basic checks	50s
Build and publish artifacts and plugins locally	1m 29s
Check service docker image contents	56s
Run annotation processor tests	1m 0s
Run sbt test	3m 4s
Maven samples (shopping-cart-quickstart, true)	41s
Maven samples (choreography-saga-quickstart, true)	50s
Maven samples (doc-snippets, false)	34s
Maven samples (view-store, true)	1m 24s
Maven samples (spring-dependency-injection, true)	59s
Maven samples (event-sourced-customer-registry, true)	1m 3s
Maven samples (event-sourced-counter-brokers, docker compose up -d, true)	1m 40s
Maven samples (event-sourced-customer-registry-subscriber, true, ./start-upstream.sh)	1m 31s
Maven samples (key-value-counter, true)	51s
Maven samples (key-value-shopping-cart, true)	51s
Maven samples (key-value-customer-registry, true)	47s
Maven samples (tracing, false)	28s
Maven samples (reliable-timers, true)	42s
Maven samples (transfer-workflow, true)	38s
Maven samples (transfer-workflow-compensation, true)	52s
	21m 10s

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