add messaging service contracts descriptions

Author: pajicf

docs/general-info/contract-addresses/testnet-contracts.md

@@ -15,6 +15,8 @@ These contracts are deployed on the Sepolia testnet. You can view them on [Sepol
 ### Bridge Contracts
 - **Rollup Contract**
   - Address: [`0x0Bf464f24D867ff0B20aE8f9C353a589138D6836`](https://sepolia.etherscan.io/address/0x0bf464f24d867ff0b20ae8f9c353a589138d6836)
+  - Purpose: Manages the L2s validity, DA and messaging from the L1 to L2
+
 - **L1 Token Bridge Proxy**
   - Address: [`0x01b44C5Ea321f921D93476cf54Aa8460db17a548`](https://sepolia.etherscan.io/address/0x01b44C5Ea321f921D93476cf54Aa8460db17a548)
   - Purpose: Manages token bridging operations on L1
@@ -39,6 +41,8 @@ These contracts are deployed on the Status Network testnet. You can view them on
 ### Bridge Contracts
 - **L2 Message Service**
   - Address: [`0xe74Bd8db0440533F8915042D980AbAA86085821c`](https://sepoliascan.status.network/address/0xe74Bd8db0440533F8915042D980AbAA86085821c)
+  - Purpose: Manages the messaging from L2 to L1
+  
 - **L2 Token Bridge Proxy**
   - Address: [`0xbC7f9571152a8e21942b2aEa4831a27f1149af19`](https://sepoliascan.status.network/address/0xbC7f9571152a8e21942b2aEa4831a27f1149af19)
   - Purpose: Manages token bridging operations on L2
@@ -56,9 +60,11 @@ These contracts are deployed on the Status Network testnet. You can view them on
 - **Multicall3**
   - Address: [`0xcA11bde05977b3631167028862bE2a173976CA11`](https://sepoliascan.status.network/address/0xcA11bde05977b3631167028862bE2a173976CA11)
   - Purpose: Batching of multiple calls to the chain from one request
+  
 - **deterministic-deployment-proxy**
   - Address: [`0x4e59b44847b379578588920cA78FbF26c0B4956C`](https://sepoliascan.status.network/address/0x4e59b44847b379578588920cA78FbF26c0B4956C)
   - Purpose: CREATE2 util contract used by popular frameworks like Hardhat and similar behind the scenes
+  
 - **safe-singleton-factory**
   - Address: [`0x914d7Fec6aaC8cd542e72Bca78B30650d45643d7`](https://sepoliascan.status.network/address/0x914d7Fec6aaC8cd542e72Bca78B30650d45643d7)
   - Purpose: Singleton factory used by Safe related contracts