fix(metrics): Bump generic extraction version (#2692)

External relays of version 23.9.1 (and possibly below) set the
`metrics_extracted` flag on transaction items even if transaction
metrics extraction is disabled:
https://github.com/getsentry/relay/blob/ffebe6020a2a6d42fde90857868736e5769a77d2/relay-server/src/actors/processor.rs#L2099-L2104

We recently [bumped](getsentry/sentry#57759)
the transaction metrics version, causing external relays to skip
extraction. But because old external relays set the `metrics_extracted`
flag anyway, even our internal PoPs skip metrics extraction now.

This PR is a one-time fix to force old external relays to stop
extracting generic metrics as well.

Author: jjbayer

CHANGELOG.md

@@ -26,6 +26,7 @@
 - Collect `http.decoded_response_content_length`. ([#2638](https://github.com/getsentry/relay/pull/2638))
 - Add TTID and TTFD tags to mobile spans. ([#2662](https://github.com/getsentry/relay/pull/2662))
 - Scrub all DB Core Data spans differently. ([#2686](https://github.com/getsentry/relay/pull/2686))
+- Support generic metrics extraction version 2. ([#2692](https://github.com/getsentry/relay/pull/2692))
 
 ## 23.10.1
 

relay-dynamic-config/src/metrics.rs

@@ -182,7 +182,9 @@ pub struct MetricExtractionConfig {
 
 impl MetricExtractionConfig {
     /// The latest version for this config struct.
-    pub const VERSION: u16 = 1;
+    ///
+    /// This is the maximum version supported by this Relay instance.
+    pub const VERSION: u16 = 2;
 
     /// Returns an empty `MetricExtractionConfig` with the latest version.
     ///