test_vm_bit_clear_on_heap_lock_blackbox: dump layer map while flaky code is running

refs https://github.com/neondatabase/neon/issues/6967

libs/pageserver_api/Cargo.toml

@@ -4,6 +4,10 @@ version = "0.1.0"
 edition.workspace = true
 license.workspace = true
 
+[features]
+default = []
+testing = []
+
 [dependencies]
 serde.workspace = true
 serde_with.workspace = true

libs/pageserver_api/src/models.rs

@@ -322,6 +322,8 @@ pub struct TenantConfig {
     pub timeline_get_throttle: Option<ThrottleConfig>,
     pub image_layer_creation_check_threshold: Option<u8>,
     pub switch_aux_file_policy: Option<AuxFilePolicy>,
+    #[cfg(feature = "testing")]
+    pub test_vm_bit_debug_logging: Option<bool>,
 }
 
 /// The policy for the aux file storage. It can be switched through `switch_aux_file_policy`