fix: broken html /docs use gfm (#3471)

docs/devs/fastapi_transition.md

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+---
+layout: default
+title: FastAPI extension upgrade
+nav_order: 1
+---
+
+## Defining a route with path parameters
+
+**old:**
+
+```python
+# with <>
+@offlineshop_ext.route("/lnurl/<item_id>", methods=["GET"])
+```
+
+**new:**
+
+```python
+# with curly braces: {}
+@offlineshop_ext.get("/lnurl/{item_id}")
+```
+
+## Check if a user exists and access user object
+
+**old:**
+
+```python
+# decorators
+@check_user_exists()
+async def do_routing_stuff():
+    pass
+```
+
+**new:**
+If user doesn't exist, `Depends(check_user_exists)` will raise an exception.
+If user exists, `user` will be the user object
+
+```python
+# depends calls
+@core_html_routes.get("/my_route")
+async def extensions(user: User = Depends(check_user_exists)):
+    pass
+```
+
+## Returning data from API calls
+
+**old:**
+
+```python
+return (
+    {
+        "id": wallet.wallet.id,
+        "name": wallet.wallet.name,
+        "balance": wallet.wallet.balance_msat
+    },
+    HTTPStatus.OK,
+)
+```
+
+FastAPI returns `HTTPStatus.OK` by default id no Exception is raised
+
+**new:**
+
+```python
+return {
+    "id": wallet.wallet.id,
+    "name": wallet.wallet.name,
+    "balance": wallet.wallet.balance_msat
+}
+```
+
+To change the default HTTPStatus, add it to the path decorator
+
+```python
+@core_app.post("/api/v1/payments", status_code=HTTPStatus.CREATED)
+async def payments():
+    pass
+```
+
+## Raise exceptions
+
+**old:**
+
+```python
+return (
+    {"message": f"Failed to connect to {domain}."},
+    HTTPStatus.BAD_REQUEST,
+)
+# or the Quart way via abort function
+abort(HTTPStatus.INTERNAL_SERVER_ERROR, "Could not process withdraw LNURL.")
+```
+
+**new:**
+
+Raise an exception to return a status code other than the default status code.
+
+```python
+raise HTTPException(
+    status_code=HTTPStatus.BAD_REQUEST,
+    detail=f"Failed to connect to {domain}."
+)
+```
+
+## Extensions
+
+**old:**
+
+```python
+from quart import Blueprint
+
+amilk_ext: Blueprint = Blueprint(
+    "amilk", __name__, static_folder="static", template_folder="templates"
+)
+```
+
+**new:**
+
+```python
+from fastapi import APIRouter
+from lnbits.jinja2_templating import Jinja2Templates
+from lnbits.helpers import template_renderer
+from fastapi.staticfiles import StaticFiles
+
+offlineshop_ext: APIRouter = APIRouter(
+    prefix="/Extension",
+    tags=["Offlineshop"]
+)
+
+offlineshop_ext.mount(
+    "lnbits/extensions/offlineshop/static",
+    StaticFiles("lnbits/extensions/offlineshop/static")
+)
+
+offlineshop_rndr = template_renderer([
+    "lnbits/extensions/offlineshop/templates",
+])
+```
+
+## Possible optimizations
+
+### Use Redis as a cache server
+
+Instead of hitting the database over and over again, we can store a short lived object in [Redis](https://redis.io) for an arbitrary key.
+Example:
+
+- Get transactions for a wallet ID
+- User data for a user id
+- Wallet data for a Admin / Invoice key