message: Use Thread Message boxel component
diff: {{#let (or milestone.complete (lte i this.workflow.completedMilestoneCount)) as |displayMilestone|}}
  {{#if displayMilestone}}
  {{#each milestone.postables as |postable j|}}
  - <div class="thread-message" data-test-thread-message={{j}} data-test-milestone={{i}}>
  - <div data-test-author>
  - {{postable.author.name}}
  - </div>
  +
  {{#if postable.message}}
  - {{format-workflow-message postable.message}}
  + <Boxel::ThreadMessage
  + @content={{format-workflow-message postable.message}}
  + data-test-thread-message={{j}} data-test-milestone={{i}}
  + />
  {{else}}
  + <Boxel::ThreadMessage
  + data-test-thread-message={{j}} data-test-milestone={{i}}
  + >
  {{component postable.componentName onComplete=(optional postable.onComplete)}}
  + </Boxel::ThreadMessage>
  {{/if}}
  + {{!-- <div class="thread-message" >
  + <div data-test-author>
  +
  </div>
  +
  + </div> --}}
  {{/each}}
  {{#if milestone.isComplete}}
  <p data-test-milestone-completed data-test-milestone={{i}}>Milestone completed: {{milestone.completedDetail}}</p>
  