feat(FastAPI): add /pkgbase/{name}/request (post)

This change implements the FastAPI version of the
/pkgbase/{name}/request form's action.

Changes from PHP:

- Additional errors are now displayed for the **merge_into** field,
  which are only displayed when the Merge type is selected.
    - If the **merge_into** field is empty, a new error is displayed:
      'The "Merge into" field must not be empty.'
    - If the **merge_into** field is given the name of a package base
      which does not exist, a new error is displayed:
      "The package base you want to merge into does not exist."
    - If the **merge_into** field is given the name of the package
      base that a request is being created for, a new error is
      displayed: "You cannot merge a package base into itself."
- When an error is encountered, users are now brought back to
  the request form which they submitted and an error is displayed
  at the top of the page.
- If an invalid type is provided, users are returned to a BAD_REQUEST
  status rendering of the request form.

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

aurweb/models/request_type.py

@@ -20,6 +20,12 @@ class RequestType(Base):
         name = self.Name
         return name[0].upper() + name[1:]
 
+    def title(self) -> str:
+        return self.name_display()
+
+    def __getitem__(self, n: int) -> str:
+        return self.Name[n]
+
 
 DELETION_ID = db.query(RequestType, RequestType.Name == DELETION).first().ID
 ORPHAN_ID = db.query(RequestType, RequestType.Name == ORPHAN).first().ID