Fature request: add a warning on clients that don't support knocking, when the room has join_rules `knock` or `knock_restricted`

**Describe the bug**

Matrix.to has ability to know the `join_rules` of a room (since https://github.com/matrix-org/matrix-spec-proposals/pull/3266), but it doesn't actually warn when a client doesn't support the feature.

**To Reproduce**
Steps to reproduce the behavior:

1. Go to a matrix.to URI link which requires knocking e.g. https://matrix.to/#/%23space.piraatit.fi:matrix.org
2. Open in Element (top option)
3. In Element attempt to join room
4. Get error: you are not invited to room

**Expected behavior**

Matrix.to sees `join_rules` being `knock` or `restricted_knock` and adds a warning to clients that don't support knocking. Knocking is a part of Matrix specification since 1.1 and `restricted_knock` I hope to soon pass the MSC process.

**Screenshots**


**Desktop (please complete the following information):**
- OS: Fedora 36
- Browser Firefox
- Version 101.0b6 (64-bittinen)

**Additional context**

* https://spec.matrix.org/latest/client-server-api/#knocking-on-rooms

Start by tracing how matrix.to handles a URI for a room with join_rules and how it identifies the selected client, then read the linked Matrix client-server API section on knocking. Done means clients that do not support knocking receive a warning for rooms using knock or restricted_knock, while supported clients remain unaffected.

Written by the indexing model from the issue text.