Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Overall the playbook uses the expression "Add the following configuration to your `inventory/host_vars/matrix.DOMAIN/vars.yml` file:" with the heading "Adjusting the playbook configuration" for sections to explain what to be added as variables

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Since upgrading mautrix-slack (and pinning to v0.1.0) in e4b54c37fe258b17f49dd7ed58a18ef3abac1c41,
we expect double-puppeting to require the new appservice double-puppeting method.

This commit switches the mautrix-slack bridge to it.