Go: add statistics command (#16119)

### What problem does this PR solve?

Prepare for enterprise command

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/cli/parser.go

@@ -138,6 +138,8 @@ func (p *Parser) parseAdminCommand() (*Command, error) {
 		return p.parseAdminSaveCommand()
 	case TokenUse:
 		return p.parseAdminUseCommand()
+	case TokenPurge:
+		return p.parseAdminPurgeCommand()
 	default:
 		return nil, fmt.Errorf("unknown command: %s", p.curToken.Value)
 	}