message: add xiaoxu as reviewer
diff: - leni-msft
  - ruowan
  - jianyexi
  + - xiaoxuqi-ms
  - rule:
  paths: "specification/@(providerhub|sql|appplatform|deviceupdate|servicelinker)/**"
  reviewers:
  - raych1
  + - xiaoxuqi-ms
  - rule:
  paths: "specification/@(security|edgeorder|synapse)/**"
  - honghr
  - tianxchen-ms
  - tadelesh
  + - xiaoxuqi-ms
  