Metrics Docs

[dingsdax]

• create user docs (see Python, Javascript)
• clarify whether to add quickstart example for your SDK
• when merged, change SDK from upcoming to supported

Metrics Feature-Issue:

• Sentry Metrics for .NET #4741

[linear]

NET-536

[Flash0ver]

Initial docs PR:

• docs(dotnet): Add metrics documentation for .NET sentry-docs#16054

[Flash0ver]

Metrics: Getting Started page:

• docs(dotnet): Add .NET to metrics getting started sentry-docs#16262

[Flash0ver]

Published Docs: https://docs.sentry.io/platforms/dotnet/metrics/

Also, added Getting-Started docs and Onboarding code snippets to Sentry

• feat(onboarding): Add metrics for .NET platforms sentry#106551
• fix(onboarding): update .NET Metrics samples to SDK v6.1.0 sentry#108034