Update Connection Proxy Settings

Enables or disables use of a connection through the Connection Proxy API. The setting is stored on the parent connection. To update proxy access for a shared connection, the caller must have edit permission for the parent connection. Enabling proxy access requires a backend that supports the Connection Proxy API. If the connection backend is unsupported, the request returns `400 Bad Request`. Disabling proxy access is allowed for any connection the caller can edit. Setting `enabled` to `false` prevents proxy calls for the connection.