feat(pretix): add ansible role and playbook

roles/pretix/README.md

@@ -0,0 +1,16 @@
+# `finallycoffee.services.pretix` ansible role
+
+
+## Troubleshooting
+
+### virtualenv
+
+By default, the virtualenv is located in `/var/lib/pretix/virtualenv`.
+This can be controlled by setting `pretix_virtualenv_dir`.
+
+NOTE: To fix a broken virtualenv, try setting `pretix_virtualenv_state` to `forcereinstall` (see
+[`ansible.builtin.pip` on docs.ansible.com](https://docs.ansible.com/ansible/latest/collections/ansible/builtin/pip_module.html)).
+
+NOTE: To install pip packages or execute migrations in the virtualenv, ansible
+needs to become the unprivilated `pretix_user` (default: `pretix`). This might
+require having the `acl` system package installed.