Fix writing promoCode file after Windows setup

[DJAndries]

Resolves brave/brave-browser#33097

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run lint, npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

If using Omaha stub:

0. Run Windows installer with a refcode embedded in the filename (i.e. BraveBrowserSetup-BRV002.exe)
1. After installation, access the local state page and search from "promo_code"
2. Ensure the promo code matches the one embedded in the filename

If using installer from CI build, see @bsclifton 's comment below

[bsclifton]

Code changes LGTM after feedback and I tested out and it works great 👍 Nice work 😄

[bsclifton]

Steps I ran to test this:

1. Grab code and build it

git fetch origin && git checkout -b windows-installer-promo-fix --track origin/windows-installer-promo-fix
npm run sync && npm run build
npm run create_dist

2. Once that finished, I created a registry entry:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\BraveSoftware\Promo]
"StubInstallerPath"="C:\\bb2\\src\\out\\Component\\BraveBrowserSetup-BSC007.exe"

This simulates the entry written by Omaha (see here for more info)

3. Went into src/out/Component directory and double clicked brave_installer.exe to manually run the mini installer
4. This created a profile directory for me at C:\Users\brian\AppData\local\BraveSoftware\Brave-Browser-Development\User Data which had the promoCode file
5. Opened promoCode file and verified it has BSC007

[kjozwiak]

Verification PASSED on Win 11 x64 using the following build(s):

Brave | 1.60.36 Chromium: 117.0.5938.88 (Official Build) nightly (64-bit)
-- | --
Revision | 4b30cbb59ae8e58bb0e529ed2459fea0fc18d5b1
OS | Windows 11 Version 22H2 (Build 22621.2283)

• downloaded https://github.com/brave/brave-browser/releases/download/v1.60.36/BraveBrowserStandaloneNightlySetup.exe
• renamed BraveBrowserStandaloneNightlySetup.exe --> BraveBrowserStandaloneNightlySetup-BSC007.exe

• launched BraveBrowserStandaloneNightlySetup-BSC007.exe and ensured promoCode was created when installing
  • opened/checked C:\Users\kamil\AppData\Local\BraveSoftware\Brave-Browser-Nightly\User Data\promoCode

Example	Example

• ensured that BSC007 is being listed/mentioned via brave://local-state as per the following:

      "referral": {
         "checked_for_promo_code_file": {
            "metadata": [ "default", "user_modifiable", "extension_modifiable" ],
            "value": false
         },
         "promo_code": {
            "metadata": [ "user_controlled", "user_modifiable", "extension_modifiable" ],
            "value": "BSC007"

I also basically went through the above using both the stub & standalone installers.