feat(STX-433): add submissionMethod to transaction metadata (#8375)

## Explanation

The goal of this PR is to add a `submissionMethod` property in the
TransactionMetadata object in order to record how the transaction was
submitted to the network and add it to the metrics. This datapoint can
be recording at submission in the
https://github.com/MetaMask/metamask-extension/blob/main/app/scripts/controller-init/confirmations/transaction-controller-init.ts

Draft PR on extension to demonstrate the use case:
MetaMask/metamask-extension#41465

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## References

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## Checklist

- [ ] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [ ] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/processes/updating-changelogs.md)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/processes/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: this is a type-only change adding an optional metadata field
and enum export, with no behavioral changes to transaction processing.
> 
> **Overview**
> Adds an optional `submissionMethod` field to `TransactionMeta` along
with a new `TransactionSubmissionMethod` enum (currently `sentinel_stx`
and `sentinel_relay`) so clients can persist how a transaction was
submitted.
> 
> Re-exports `TransactionSubmissionMethod` from the package entrypoint
and documents the addition in the `transaction-controller` changelog.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
dd12d37. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: rarquevaux

packages/transaction-controller/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Add optional `submissionMethod` property and `TransactionSubmissionMethod` enum to `TransactionMeta` ([#8375](https://github.com/MetaMask/core/pull/8375))
+
 ### Changed
 
 - Bump `@metamask/accounts-controller` from `^37.1.1` to `^37.2.0` ([#8363](https://github.com/MetaMask/core/pull/8363))

packages/transaction-controller/src/index.ts

@@ -123,6 +123,7 @@ export {
   TransactionContainerType,
   TransactionEnvelopeType,
   TransactionStatus,
+  TransactionSubmissionMethod,
   TransactionType,
   UserFeeLevel,
   WalletDevice,

packages/transaction-controller/src/types.ts

@@ -574,6 +574,11 @@ export type TransactionMeta = {
     error: string;
     message: string;
   };
+
+  /**
+   * The method used to submit the transaction to the network.
+   */
+  submissionMethod?: TransactionSubmissionMethod;
 };
 
 /**
@@ -640,6 +645,14 @@ export type SendFlowHistoryEntry = {
   timestamp: number;
 };
 
+/**
+ * The method used to submit a transaction to the network.
+ */
+export enum TransactionSubmissionMethod {
+  SentinelStx = 'sentinel_stx',
+  SentinelRelay = 'sentinel_relay',
+}
+
 /**
  * Represents the status of a transaction within the wallet.
  * Each status reflects the state of the transaction internally,