feat: client and server logic to manage announcements (#3)

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Reviewed-on: #3
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

client/src/app/announcements/announcements.html

@@ -0,0 +1,20 @@
+<h1>Announcements</h1>
+<p>Here are the most recent updates for our products and communities.</p>
+<p>
+  If you want to see the full history, check out our
+  <a href="https://chat.nhcarrigan.com" target="_blank">chat server</a> or our
+  <a href="https://forum.nhcarrigan.com" target="_blank">forum</a>.
+</p>
+<div class="announcement" *ngFor="let announcement of announcements">
+  <hr />
+  <h2>{{ announcement.title }}</h2>
+  <p>
+    <span [class]="'tag ' + announcement.type">{{announcement.type}}</span>
+    <span class="date"> {{ announcement.createdAt | date: "mediumDate" }}</span>
+  </p>
+  <markdown [data]="announcement.content"></markdown>
+  <p class="type">Type: {{ announcement.type }}</p>
+</div>
+<div class="no-announcements" *ngIf="!announcements.length">
+  <p>There are no announcements at this time.</p>
+</div>