Preserve white space in text plugin. (#6833)

Some users require the spaces to be preserved in the text shown in the
text dashboard.

At the moment I can't think of a reason why not to enable this
unconditionally. I imagine anybody interested in seeing text logged
would be interested in the value *verbatim*, including spaces.

Googlers, see b/335770352

tensorboard/components/tf_markdown_view/tf-markdown-view.ts

@@ -46,6 +46,12 @@ class TfMarkdownView extends LegacyElementMixin(PolymerElement) {
       #markdown > p:last-child {
         margin-bottom: 0.3em;
       }
+      #markdown p {
+        /* Some users include multiple spaces and would like them preserved in
+         * the text visualization in TB. Googlers, see b/335770352.
+         */
+        white-space: break-spaces;
+      }
 
       /* Pleasant styles for Markdown tables. */
       #markdown table {