feat: adding docs for payment metadata (#124)

Co-authored-by: vacwmX <vacwm01@gmail.com>
Co-authored-by: ok300 <106775972+ok300@users.noreply.github.com>

snippets/rust/src/metadata.rs

@@ -0,0 +1,73 @@
+use std::sync::Arc;
+use anyhow::Result;
+use breez_sdk_core::*;
+
+async fn set_payment_metadata(sdk: Arc<BreezServices>) -> Result<()> {
+  // ANCHOR: set-payment-metadata
+    sdk.set_payment_metadata("target-payment-hash", r#"{"myCustomValue":true}"#).await?;
+  // ANCHOR_END: set-payment-metadata
+  
+    Ok(())
+}
+
+async fn filter_payment_metadata(sdk: Arc<BreezServices>) -> Result<()> {
+  // ANCHOR: filter-payment-metadata
+    let metadata_filters = vec![
+        MetadataFilter {
+            json_path: "myCustomValue".to_string(),
+            json_value: "true".to_string(),
+        },
+    ];
+
+    sdk.list_payments(ListPaymentsRequest {
+        metadata_filters,
+        ..Default::default(),
+    }).await?;
+  // ANCHOR_END: filter-payment-metadata
+}
+
+async fn filter_payment_metadata_string(sdk: Arc<BreezServices>) -> Result<()> {
+  // ANCHOR: filter-payment-metadata-string
+    // Note: The following are equivalent
+    let metadata_filters = vec![
+        MetadataFilter {
+            json_path: "customerName".to_string(),
+            json_value: r#""Satoshi Nakamoto""#.to_string(),
+        },
+        MetadataFilter {
+            json_path: "customerName".to_string(),
+            json_value: serde_json::json!("Satoshi Nakamoto").to_string(),
+        },
+    ];
+  // ANCHOR_END: filter-payment-metadata-string
+}
+
+async fn filter_payment_metadata_object(sdk: Arc<BreezServices>) -> Result<()> {
+  // ANCHOR: filter-payment-metadata-object
+    // This will *NOT* work
+    let metadata_filters = vec![
+        MetadataFilter {
+            json_path: "parent.nestedArray".to_string(),
+            json_value: r#"[1, 2, 3]"#.to_string(),
+        },
+    ];
+
+    // Any of these will work
+    let metadata_filters = vec![
+        MetadataFilter {
+            json_path: "parent.nestedArray".to_string(),
+            json_value: r#"[1,2,3]"#.to_string(),
+        },
+    ];
+  // ANCHOR_END: filter-payment-metadata-object
+  
+  // ANCHOR: filter-payment-metadata-object-serde
+    let metadata_filters = vec![
+        MetadataFilter {
+            json_path: "parent.nestedArray".to_string(),
+            json_value: serde_json::json!(&[1, 2, 3]).to_string(),
+        },
+    ];
+  // ANCHOR_END: filter-payment-metadata-object-serde
+    Ok(())
+}