Implement instance info endpoint (JSON, YAML, TXT) (#685)

Co-authored-by: Daniel Valentine <daniel@vielle.ws>
Co-authored-by: spikecodes <19519553+spikecodes@users.noreply.github.com>

templates/message.html

@@ -0,0 +1,10 @@
+{% extends "base.html" %}
+{% block title %}{{ title }}{% endblock %}
+{% block sortstyle %}{% endblock %}
+{% block content %}
+	<div id="message">
+		<h1>{{ title }}</h1>
+		<br>
+		{{ body|safe }}
+	</div>
+{% endblock %}