docs: add metrics to attribute documentation

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: jpnurmi

include/sentry.h

@@ -1863,6 +1863,7 @@ SENTRY_API void sentry_remove_extra_n(const char *key, size_t key_len);
  * Sets attributes created with `sentry_value_new_attribute` to be applied to
  * all:
  * - logs
+ * - metrics
  */
 SENTRY_API void sentry_set_attribute(const char *key, sentry_value_t attribute);
 SENTRY_API void sentry_set_attribute_n(