proxies: add smart proxy support

still to do:

* document new configuration options
* add smart proxies to groups view
* import bandwidth and CPU alarms

app/portal/smart_proxy.py

@@ -0,0 +1,17 @@
+from flask import render_template, Blueprint
+from flask.typing import ResponseReturnValue
+from sqlalchemy import desc
+
+from app.models.mirrors import SmartProxy
+
+bp = Blueprint("smart_proxy", __name__)
+
+
+@bp.route("/list")
+def smart_proxy_list() -> ResponseReturnValue:
+    instances = SmartProxy.query.filter(SmartProxy.destroyed.is_(None)).order_by(desc(SmartProxy.added)).all()
+    return render_template("list.html.j2",
+                           section="smart_proxy",
+                           title="Smart Proxy Instances",
+                           item="smart proxy",
+                           items=instances)