title: Customize WP block gallery
body: <p>Is there any option to change the output of the WP block gallery component in Gutenberg editor?
  Currently I set some images with external links (link to media attachment) and I get this result:</p>
  
  <pre><code>&lt;ul class="wp-block-gallery columns-2"&gt;
      &lt;li class="blocks-gallery-item"&gt;
          &lt;figure&gt;
              &lt;a href="..."&gt;
                  &lt;img src="..." alt="" data-id="" data-link="" class=""&gt;
              &lt;/a&gt;
              &lt;figcaption&gt;Some text&lt;/figcaption&gt;
          &lt;/figure&gt;
      &lt;/li&gt;
      &lt;li class="blocks-gallery-item"&gt;
          &lt;figure&gt;
              &lt;a href="..."&gt;
                  &lt;img src="..." alt="" data-id="" data-link="" class=""&gt;
              &lt;/a&gt;
              &lt;figcaption&gt;Some text&lt;/figcaption&gt;
          &lt;/figure&gt;
      &lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>But I want to also set the title attribute for anchor element. This is the result that I want:</p>
  
  <pre><code>&lt;ul class="wp-block-gallery columns-2"&gt;
      &lt;li class="blocks-gallery-item"&gt;
          &lt;figure&gt;
              &lt;a href="..." title="some title"&gt;
                  &lt;img src="..." alt="" data-id="" data-link="" class=""&gt;
              &lt;/a&gt;
              &lt;figcaption&gt;Some text&lt;/figcaption&gt;
          &lt;/figure&gt;
      &lt;/li&gt;
      &lt;li class="blocks-gallery-item"&gt;
          &lt;figure&gt;
              &lt;a href="..." title="some title"&gt;
                  &lt;img src="..." alt="" data-id="" data-link="" class=""&gt;
              &lt;/a&gt;
              &lt;figcaption&gt;Some text&lt;/figcaption&gt;
          &lt;/figure&gt;
      &lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>Thanks</p>