feat(mr): log when txs are sent

Has the Message Relayer log transaction hashes when transactions are
sent.

.changeset/thin-moles-learn.md

+---
+'@eth-optimism/message-relayer': patch
+---
+
+Update message relayer to log sent tx hashes

packages/message-relayer/src/service.ts

@@ -162,7 +162,8 @@ export class MessageRelayerService extends BaseService<MessageRelayerOptions> {
           // each message to L1.
           for (const message of messages) {
             try {
-              await this.state.messenger.finalizeMessage(message)
+              const tx = await this.state.messenger.finalizeMessage(message)
+              this.logger.info(`relayer sent tx: ${tx.hash}`)
             } catch (err) {
               if (err.message.includes('message has already been received')) {
                 // It's fine, the message was relayed by someone else