[CODEOWNERS] No entry for mooncake-p2p-store

## Description

`.github/CODEOWNERS` currently has no entry for `mooncake-p2p-store/`, so PRs touching only that directory get no reviewer auto-assigned and can sit unnoticed.

Example: #2375 (Go bugfix, only touches `mooncake-p2p-store/`) has been open since Jun 8 with green CI but never had a reviewer requested — every other directory in that PR-batch got auto-assignment via CODEOWNERS.

## Suggestion

Add an entry such as:

```
/mooncake-p2p-store
```

Leaving the owner choice to the maintainers — happy to send the one-line PR once owners are decided.

Start by inspecting .github/CODEOWNERS and comparing its directory entries with the paths in PR #2375. Confirm which owners maintainers want for mooncake-p2p-store/, then add the directory entry and verify that the CODEOWNERS syntax matches the surrounding entries.

Written by the indexing model from the issue text.