title: debounceTime only after first value
body: <p>Is there a simple way to make debounceTime instant on the first value?</p>
  
  <pre><code>searchQueries.pipe(debounceTime(1000))
  </code></pre>
  
  <p>let's say i'm debouncing search queries to 1 second.</p>
  
  <p>My understanding is that this will cause a 1 second delay on the first search, But, I want the first search query to be instant.</p>
  
  <p>(e.g. in this example <a href="https://stackblitz.com/edit/typescript-adheqt?file=index.ts&amp;devtoolsheight=50" rel="noreferrer">https://stackblitz.com/edit/typescript-adheqt?file=index.ts&amp;devtoolsheight=50</a> if i type 123 quickly, it will only log 123, but i want it to log 1 and then log 123)</p>
  
  <p>i could try something like</p>
  
  <pre><code>merge(searchQueries.pipe(first()),searchQueries.pipe(debounceTime(1000)))
  </code></pre>
  
  <p>but then that would potentially add a delay to a second search but is probably good enough.</p>
  
  <p>Is there a way of configuring debounceTime that i'm missing? or should I potentially be using throttle or something else?</p>