feat(envelope-item): Support metric type #6224

Job	Run time
system-test (sentry-samples-spring-boot, false, true)	25s
system-test (sentry-samples-spring-boot-opentelemetry-noagent, false, true)	29s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry, true, false)	38s
system-test (sentry-samples-spring-boot-opentelemetry, true, false)	28s
system-test (sentry-samples-spring-boot-jakarta, false, true)	25s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry-noagent, false, true)	25s
system-test (sentry-samples-spring-boot-webflux, false, true)	41s
system-test (sentry-samples-spring-boot-opentelemetry, true, true)	41s
system-test (sentry-samples-log4j2, false, true)	24s
system-test (sentry-samples-spring-boot-webflux-jakarta, false, true)	25s
system-test (sentry-samples-spring-boot-4-opentelemetry, true, false)	25s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry, true, true)	25s
system-test (sentry-samples-console, false, true)	38s
system-test (sentry-samples-logback, false, true)	25s
system-test (sentry-samples-jul, false, true)	42s
system-test (sentry-samples-spring-jakarta, false, true)	26s
system-test (sentry-samples-spring-7, false, true)	38s
system-test (sentry-samples-spring-boot-4-webflux, false, true)	25s
system-test (sentry-samples-spring, false, true)	26s
system-test (sentry-samples-spring-boot-4-opentelemetry, true, true)	26s
system-test (sentry-samples-spring-boot-4, false, true)	27s
	10m 24s

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