message: add `accountLinkingHeader` to ring account linking component
diff: <h4 class="text-center primary-text mb-3"
  translate="plugins.settings.custom.homebridge-gsh.label_link_account"></h4>
  + <markdown hrefTargetBlank class="plugin-md" [data]="schema.accountLinkingHeader" *ngIf="schema.accountLinkingHeader">
  + </markdown>
  +
  <div [hidden]="doingLogin" class="card p-3">
  <ng-container *ngIf="!twoFactorRequired">
  <div class="form-group">
  <input formControlName="twoFactorAuthCode" type="text" class="form-control" id="ringVerificationCode"
  autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false">
  <small id="ringVerificationCodeHelp" class="form-text text-muted">
  - Please enter the code sent to phone ending in XX{{ phoneLastTwo }}
  + Please enter the code sent to phone {{ phoneLastTwo }}
  </small>
  </div>
  <div class="text-center">
  