title: Replace fluentd string using regex
body: <p>When sending logs, I want to replace the <code>id</code> and <code>pw</code> values as in:</p>
  
  <pre><code>https://m.xxxxx.com/yyyy.xxxx?id=aaaa&amp;pw=cccc
  https://m.xxxxx.com/aaaa.xxxx?id=aaaa&amp;pass=cccc
  </code></pre>
  
  <p>with different values such as:</p>
  
  <pre><code>https://m.xxxxx.com/yyyy.xxxx?id=*&amp;pw=****
  https://m.xxxxx.com/aaaa.xxxx?id=*&amp;pass=****
  </code></pre>
  
  <p>It is difficult to create a plugin. Is it possible to transfer by converting the <code>id = aaaa</code> value to <code>id = ****</code> using existing <code>filter_record_transformer</code> or <code>grep</code>? Is it impossible to use <code>gsub</code> of <code>filter_record_transformer</code>?</p>