[No QA] Docs updates for E/A#97811 Add Vendor action field to Merchant Rules

[MelvinBot]

Summary

Documents the new Vendor action field on Merchant Rules, added to NewDot in #97811 (vendor matching R5, Phase B).

That PR lets Workspace Admins set a specific vendor on every expense a Merchant Rule matches, so non-reimbursable company card expenses export with the correct vendor. The field is labeled Supplier on Xero workspaces and is available only on workspaces connected to QuickBooks Online, Sage Intacct, or Xero. The existing QuickBooks Online vendor matching article already references "if a workspace merchant rule specifies a vendor," but the Merchant Rules article did not yet document this field — this PR closes that gap.

Changes to Workspace-Merchant-Rules.md

• Added vendors to the intro list of fields Merchant Rules can update.
• Added a bullet under What can you do with Merchant Rules? for setting the vendor used on export.
• Added Vendor to the What expense fields can be updated by Merchant Rules? list, noting the connected-integration requirement.
• Added a new FAQ, How does the Vendor field on a Merchant Rule work?, covering the QBO/Sage Intacct/Xero requirement, the Supplier label on Xero, the priority over automatic vendor matching, and how to set it.
• Added vendor/supplier SEO keywords to the frontmatter.

Notes for the reviewer

• In [Payment due @abzokhattab] Add vendorID action field to merchant coding rules (vendor matching R5, Phase B) #97811 this feature is gated behind the vendorMatching beta in addition to the connected-integration requirement. The docs do not mention the beta (matching the precedent of the already-published QBO vendor matching article). If the feature is not yet generally available, please hold this PR until GA.
• UI labels used here (Vendor / Supplier, Save rule) were verified against src/languages/en.ts and the PR's UI code (common.vendor, common.supplier), since the beta gate prevents surfacing the field in the standard test session.

---

@Beamanator, please review the files changed and confirm they reflect the current behavior. Then post a new comment saying @MelvinBot mark this PR as ready for review.

[MelvinBot]

There's nothing to fix here — no code check is failing.

The only red check is Check independent approval, which isn't a build/test failure. It fails simply because the PR hasn't received an independent approval yet; it clears automatically once a reviewer other than the author approves. Every actual CI check is green: check, dryRun, spellcheck, validate, verify, verifySignedCommits, and CLA.

So no push is needed. To turn this check green, this PR just needs an independent review/approval.

[OSBotify]

A preview of your ExpensifyHelp changes have been deployed to https://abb6d049.helpdot.pages.dev ⚡️

Updated articles:

• articles/new-expensify/workspaces/Workspace-Merchant-Rules