feat(FastAPI): add /requests/{id}/close (get, post)

Changes from PHP:

- If a user submits a POST request with an invalid reason,
  they are returned back to the closure form with a BAD_REQUEST status.
- Now, users which created a PackageRequest have the ability to close
  their own.
- Form action has been changed to `/requests/{id}/close`.

Closes https://gitlab.archlinux.org/archlinux/aurweb/-/issues/20

Signed-off-by: Kevin Morris <kevr@0cost.org>

templates/requests/close.html

@@ -0,0 +1,60 @@
+{% extends "partials/layout.html" %}
+
+{% block pageContent %}
+    <div class="box">
+        <h2>{{ "Close Request" | tr }}: {{ pkgreq.PackageBaseName }}</h2>
+
+        <p>
+            {{
+                "Use this form to close the request for package base %s%s%s."
+                | tr | format("<strong>", pkgreq.PackageBaseName, "</strong>")
+                | safe
+            }}
+        </p>
+
+        <p>
+            <em>{{ "Note" | tr }}:</em>
+            {{
+                "The comments field can be left empty. However, it is highly "
+                "recommended to add a comment when rejecting a request."
+                | tr
+            }}
+        </p>
+
+        <form action="/requests/{{ pkgreq.ID }}/close" method="post">
+            <fieldset>
+                <p>
+                    <label for="id_reason">{{ "Reason" | tr }}:</label>
+                    <select id="id_reason" name="reason">
+                        {# Value 2 == "Accepted" status.
+                        See aurweb.models.package_request. #}
+                        {% if request.user.is_elevated() %}
+                            <option value="2">
+                                {{ "Accepted" | tr }}
+                            </option>
+                        {% endif %}
+                        {# Value 3 == "Rejected" status.
+                        See aurweb.models.package_request. #}
+                        <option value="3">
+                            {{ "Rejected" | tr }}
+                        </option>
+                    </select>
+                </p>
+
+                <p>
+                    <label for="id_comments">{{ "Comments" | tr }}:</label>
+                    <textarea id="id_comments" name="comments"
+                              rows="5" cols="50"></textarea>
+                </p>
+
+                <p>
+                    <button class="button" type="submit">
+                        {{ "Close Request" | tr }}
+                    </button>
+                </p>
+
+            </fieldset>
+        </form>
+
+    </div>
+{% endblock %}