[PM-14899] Update CODEOWNERS to have Platform as default (#196)

## 🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-14899

## 📔 Objective

We want Platform to be the default CODEOWNER for `sdk-internal`. This
will be temporary, and we'll add additional teams as we onboard them
into the SDK.

## ⏰ Reminders before review

- Contributor guidelines followed
- All formatters and local linters executed and passed
- Written new unit and / or integration tests where applicable
- Protected functional changes with optionality (feature flags)
- Used internationalization (i18n) for all UI strings
- CI builds passed
- Communicated to DevOps any deployment requirements
- Updated any necessary documentation (Confluence, contributing docs) or
informed the documentation
  team

## 🦮 Reviewer guidelines

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- 👍 (`:+1:`) or similar for great changes
- 📝 (`:memo:`) or ℹ️ (`:information_source:`) for notes or general info
- ❓ (`:question:`) for questions
- 🤔 (`:thinking:`) or 💭 (`:thought_balloon:`) for more open inquiry
that's not quite a confirmed
  issue and could potentially benefit from discussion
- 🎨 (`:art:`) for suggestions / improvements
- ❌ (`:x:`) or ⚠️ (`:warning:`) for more significant problems or
concerns needing attention
- 🌱 (`:seedling:`) or ♻️ (`:recycle:`) for future improvements or
indications of technical debt
- ⛏ (`:pick:`) for minor or nitpick changes

Author: trmartin4

.github/CODEOWNERS

@@ -4,6 +4,9 @@
 #
 # https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
 
+# Platform is the default owner for all files
+* @bitwarden/team-platform-dev
+
 # BRE for publish workflow changes
 .github/workflows/publish-*.yml @bitwarden/dept-bre
 .github/workflows/release-rust-crates.yml @bitwarden/dept-bre