Add metadata retrieved from the `context` to the user agent when a new HTTP client is created #5080

Job	Run time
run-determination	1s
check-outdated (./)	10s
check-license-headers (./)	13s
check-config (./)	9s
check-formatting (./)	8s
check-style (./)	1m 3s
build (internal/arduino/discovery/discovery_client)	16s
build (rpc/internal/client_example)	24s
build (commands/term_example)	22s
	2m 46s

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