Support Transaction info source

[marandaneto]

Docs: https://develop.sentry.dev/sdk/event-payloads/transaction/#transaction-annotations (PR: getsentry/develop#624)
JS SDK issue

Right now this is only needed if you have a transaction's name with high cardinality which isn't the case right now.
Eventually, we need to add this.

We need to add this when we expect metrics to be extracted from transactions. In other words, this is a requirements to Metrics Enhanced Performance

Only the JS SDK is now being flagged as requiring this value. That said, we still want to add this to the protocol and change all SDKs going forward. It isn't a blocker for dynamic sampling LA.

• Java/Android Send source for transactions sentry-java#2180
• .NET / Unity Add TransactionNameSource annotation sentry-dotnet#1910
• Cocoa Add transaction source sentry-cocoa#2075
• Dart
• React Native
• Capacitor

[bruno-garcia]

@marandaneto that doesn't seem to be a big deal for Mobile since the transaction names are generally of good quality, right? We have the view name, for example. It's more for server where you end up with a raw URL, if u don't have the routing template

Updated the description.