Add pretend authenticated API for govuk-alerts

We can define the API properly in future work. I've used a separate
blueprint from "broadcasts" since this API is purely internal, and
it's helpful to make it clear it's specific to govuk-alerts.

app/v2/govuk_alerts/__init__.py

@@ -0,0 +1,11 @@
+from flask import Blueprint
+
+from app.v2.errors import register_errors
+
+v2_govuk_alerts_blueprint = Blueprint(
+    "v2_govuk-alerts_blueprint",
+    __name__,
+    url_prefix='/v2/govuk-alerts',
+)
+
+register_errors(v2_govuk_alerts_blueprint)

app/v2/govuk_alerts/get_broadcasts.py

@@ -0,0 +1,8 @@
+from flask import jsonify
+
+from app.v2.govuk_alerts import v2_govuk_alerts_blueprint
+
+
+@v2_govuk_alerts_blueprint.route('')
+def get_broadcasts():
+    return jsonify({})