Add receive_ephemeral everywhere de.sorunome.msc2409.push_ephemeral is used

Ref:

- https://github.com/mautrix/go/blob/33f3ccd6aef0a3ef3a37fefead208c6249169142/CHANGELOG.md#L134-L136
- https://github.com/mautrix/go/blob/7165d3fa583444352ea770b5c003c93a7fc6989c/appservice/registration.go#L30

Intentionally not removing the old configuration setting yet, as some bridges may/do not support
the new setting name. It's likely just bridgev2 mautrix bridges that have been updated and support both right now.

docs/configuring-playbook-conduit.md

@@ -65,6 +65,7 @@ Find the `registration.yaml` in the `/matrix` directory, for example `/matrix/ma
     ```
     as_token: <token>
     de.sorunome.msc2409.push_ephemeral: true
+    receive_ephemeral: true
     hs_token: <token>
     id: signal
     namespaces:

docs/configuring-playbook-conduwuit.md

@@ -83,6 +83,7 @@ Then, send its content to the existing admin room:
     ```
     as_token: <token>
     de.sorunome.msc2409.push_ephemeral: true
+    receive_ephemeral: true
     hs_token: <token>
     id: signal
     namespaces: