feat(envelope-item): Support metric type #6225

Job	Run time
system-test (sentry-samples-spring-boot-jakarta, false, true)	5m 0s
system-test (sentry-samples-spring-boot-opentelemetry, true, true)	4m 57s
system-test (sentry-samples-spring-boot-opentelemetry, true, false)	5m 1s
system-test (sentry-samples-spring-boot-webflux-jakarta, false, true)	4m 3s
system-test (sentry-samples-spring-boot-opentelemetry-noagent, false, true)	5m 2s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry-noagent, false, true)	5m 1s
system-test (sentry-samples-spring-boot-webflux, false, true)	4m 17s
system-test (sentry-samples-spring-boot, false, true)	4m 23s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry, true, true)	5m 1s
system-test (sentry-samples-console, false, true)	2m 14s
system-test (sentry-samples-spring-boot-4, false, true)	3m 50s
system-test (sentry-samples-spring-boot-4-webflux, false, true)	5m 1s
system-test (sentry-samples-jul, false, true)	2m 3s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry, true, false)	4m 58s
system-test (sentry-samples-spring-boot-4-opentelemetry, true, true)	4m 56s
system-test (sentry-samples-logback, false, true)	2m 12s
system-test (sentry-samples-spring-7, false, true)	4m 41s
system-test (sentry-samples-spring-jakarta, false, true)	4m 23s
system-test (sentry-samples-spring-boot-4-opentelemetry, true, false)	5m 2s
system-test (sentry-samples-spring, false, true)	4m 6s
system-test (sentry-samples-log4j2, false, true)	2m 25s
	1h 28m 36s

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