Custom measurements API

[marandaneto]

Users should be able to:

void Transaction#setMeasurement(String name, num value, {SentryMeasurementUnit? unit})
transaction.setMeasurement('name', 10, unit: SentryMeasurementUnit.milliseconds);

When the transaction is finished, setting a custom measurement is a no-op; see getsentry/sentry-dart#1026.

Depends on
#31

Spec https://develop.sentry.dev/sdk/event-payloads/transaction/

DACI https://www.notion.so/sentry/Custom-Measurements-Units-Protocol-7d3752b43bb946bf87d96e401268ca02

• Dart
• Android
• feat: Custom measurements API sentry-cocoa#2268
• React Native
• .NET

Patch the docs and add code snippets https://github.com/getsentry/sentry-docs/edit/master/src/platforms/common/performance/instrumentation/performance-metrics.mdx

[mattjohnsonpint]

We need to update the list of SDKs and versions that support this in the docs here:
https://docs.sentry.io/product/performance/metrics/#custom-performance-metrics

[marandaneto]

We need to update the list of SDKs and versions that support this in the docs here: docs.sentry.io/product/performance/metrics/#custom-performance-metrics

good catch, I was not aware of this list, would you mind adding the missing SDKs? RN, Cocoa, Dart, and Android together with .NET?

[mattjohnsonpint]

Yes. I'll start a draft PR for that and merge after the .NET SDK releases later today/tomorrow.

[mattjohnsonpint]

Docs PR: getsentry/sentry-docs#5689

I didn't add React Native though, because its docs page for custom metrics is showing the default page for Javascript. Is that accurate? Or does it need its own? And if so, what version, etc? @krystofwoldrich
https://docs.sentry.io/platforms/react-native/performance/instrumentation/performance-metrics/

[marandaneto]

Docs PR: getsentry/sentry-docs#5689

I didn't add React Native though, because its docs page for custom metrics is showing the default page for Javascript. Is that accurate? Or does it need its own? And if so, what version, etc? @krystofwoldrich docs.sentry.io/platforms/react-native/performance/instrumentation/performance-metrics

The RN SDK inherits the docs from JS most of the time because they are the same, but this one should have its own because it has the JS SDK version instead of the RN version.
@krystofwoldrich let's do this quick fix.
RN SDK bundles the JS SDK v7 from 4.0.0

[mattjohnsonpint]

I added RN 4.0.0 to the list in my PR, but there should be a separate docs PR to fix up that page. I'm not sure if you need other stuff for RN or just the version number.