[bridge] report last_observed_actions_seq_num metrics (#20024)

## Description 

as title

## Test plan 

How did you test the new or updated feature?

---

## Release notes

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your changes, release notes aren't required.

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that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:
- [ ] REST API:

crates/sui-bridge/Cargo.toml

@@ -12,6 +12,7 @@ tokio = { workspace = true, features = ["full"] }
 sui-types.workspace = true
 sui-authority-aggregation.workspace = true
 arc-swap.workspace = true
+strum_macros.workspace = true
 num_enum.workspace = true
 move-core-types.workspace = true
 url.workspace = true

crates/sui-bridge/src/metrics.rs

@@ -103,6 +103,8 @@ pub struct BridgeMetrics {
     pub(crate) action_executor_execution_queue_received_actions: IntCounter,
     pub(crate) action_executor_execution_queue_skipped_actions_due_to_pausing: IntCounter,
 
+    pub(crate) last_observed_actions_seq_num: IntGaugeVec,
+
     pub(crate) signer_with_cache_hit: IntCounterVec,
     pub(crate) signer_with_cache_miss: IntCounterVec,
 
@@ -293,6 +295,13 @@ impl BridgeMetrics {
                 registry,
             )
             .unwrap(),
+            last_observed_actions_seq_num: register_int_gauge_vec_with_registry!(
+                "bridge_last_observed_actions_seq_num",
+                "The latest observed action sequence number per chain_id and action_type",
+                &["chain_id", "action_type"],
+                registry,
+            )
+            .unwrap(),
             signer_with_cache_hit: register_int_counter_vec_with_registry!(
                 "bridge_signer_with_cache_hit",
                 "Total number of hit in signer's cache, by verifier type",

crates/sui-bridge/src/orchestrator.rs

@@ -160,6 +160,10 @@ where
                 if let Some(action) = bridge_event
                     .try_into_bridge_action(sui_event.id.tx_digest, sui_event.id.event_seq as u16)
                 {
+                    metrics.last_observed_actions_seq_num.with_label_values(&[
+                        action.chain_id().to_string().as_str(),
+                        action.action_type().to_string().as_str(),
+                    ]);
                     actions.push(action);
                 }
             }
@@ -238,7 +242,13 @@ where
                     .expect("Sending event to monitor channel should not fail");
 
                 match bridge_event.try_into_bridge_action(log.tx_hash, log.log_index_in_tx) {
-                    Ok(Some(action)) => actions.push(action),
+                    Ok(Some(action)) => {
+                        metrics.last_observed_actions_seq_num.with_label_values(&[
+                            action.chain_id().to_string().as_str(),
+                            action.action_type().to_string().as_str(),
+                        ]);
+                        actions.push(action)
+                    }
                     Ok(None) => {}
                     Err(e) => {
                         error!(eth_tx_hash=?log.tx_hash, eth_event_index=?log.log_index_in_tx, "Error converting EthBridgeEvent to BridgeAction: {:?}", e);

crates/sui-bridge/src/types.rs

@@ -23,6 +23,7 @@ use serde::{Deserialize, Serialize};
 use shared_crypto::intent::IntentScope;
 use std::collections::{BTreeMap, BTreeSet};
 use std::fmt::Debug;
+use strum_macros::Display;
 use sui_types::base_types::SuiAddress;
 use sui_types::bridge::{
     BridgeChainId, MoveTypeTokenTransferPayload, APPROVAL_THRESHOLD_ADD_TOKENS_ON_EVM,
@@ -201,7 +202,7 @@ impl CommitteeTrait<BridgeAuthorityPublicKeyBytes> for BridgeCommittee {
     }
 }
 
-#[derive(Serialize, Copy, Clone, PartialEq, Eq, TryFromPrimitive, Hash)]
+#[derive(Serialize, Copy, Clone, PartialEq, Eq, TryFromPrimitive, Hash, Display)]
 #[repr(u8)]
 pub enum BridgeActionType {
     TokenTransfer = 0,

crates/sui-types/src/bridge.rs

@@ -1,14 +1,6 @@
 // Copyright (c) Mysten Labs, Inc.
 // SPDX-License-Identifier: Apache-2.0
 
-use enum_dispatch::enum_dispatch;
-use move_core_types::ident_str;
-use move_core_types::identifier::IdentStr;
-use num_enum::TryFromPrimitive;
-use schemars::JsonSchema;
-use serde::{Deserialize, Serialize};
-use serde_with::serde_as;
-
 use crate::base_types::ObjectID;
 use crate::base_types::SequenceNumber;
 use crate::collection_types::LinkedTableNode;
@@ -26,6 +18,14 @@ use crate::{
     error::SuiError,
     id::UID,
 };
+use enum_dispatch::enum_dispatch;
+use move_core_types::ident_str;
+use move_core_types::identifier::IdentStr;
+use num_enum::TryFromPrimitive;
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+use serde_with::serde_as;
+use strum_macros::Display;
 
 pub type BridgeInnerDynamicField = Field<u64, BridgeInnerV1>;
 pub type BridgeRecordDyanmicField = Field<
@@ -71,7 +71,17 @@ pub const TOKEN_ID_USDC: u8 = 3;
 pub const TOKEN_ID_USDT: u8 = 4;
 
 #[derive(
-    Debug, Serialize, Deserialize, PartialEq, Eq, Clone, Copy, TryFromPrimitive, JsonSchema, Hash,
+    Debug,
+    Serialize,
+    Deserialize,
+    PartialEq,
+    Eq,
+    Clone,
+    Copy,
+    TryFromPrimitive,
+    JsonSchema,
+    Hash,
+    Display,
 )]
 #[repr(u8)]
 pub enum BridgeChainId {