Introduce a data_dir variable for pottwal

We've had too many confusions about the actual data directory and
unfortunately there are also inconsistencies. So use the data_dir
variable to mask host specific settings.

pottwal.yml

@@ -5,8 +5,11 @@
   vars:
     ansible_python_interpreter: /usr/bin/python3
 
+    data_dir: "/srv/data"
+
+
     openhab_image: openhab/openhab:2.5.11
-    openhab_data: /srv/data/openhab
+    openhab_data: "{{ data_dir }}/openhab"
     openhab_host_port: 8081
     openhab_configuration_source: https://github.com/netz39/n39-openhab.git
     openhab_configuration_version: master
@@ -30,7 +33,7 @@
 
     - name: Check if gitea data dir exists
       ansible.builtin.stat:
-        path: "/srv/data/gitea"
+        path: "{{ data_dir }}/gitea"
       register: gitea_dir
     - name: Fail if gitea data dir does not exist
       ansible.builtin.fail:
@@ -62,7 +65,7 @@
           USER_UID=1000
           USER_GID=1000
         volumes:
-          - "/srv/data/gitea:/data:rw"
+          - "{{ data_dir }}/gitea:/data:rw"
 
     - name: Setup proxy site gitea.n39.eu
       include_role:
@@ -187,7 +190,7 @@
 
     - name: Check if hedgedoc data dir exists
       ansible.builtin.stat:
-        path: "/srv/data/hedgedoc"
+        path: "{{ data_dir }}/hedgedoc"
       register: hedgedoc_dir
     - name: Fail if hedgedoc data dir does not exist
       ansible.builtin.fail:
@@ -199,8 +202,8 @@
         path: "{{ item }}"
         state: directory
       with_items:
-        - "/srv/data/hedgedoc/data/database"
+        - "{{ data_dir }}/hedgedoc/data/database"
-        - "/srv/data/hedgedoc/data/uploads"
+        - "{{ data_dir }}/hedgedoc/data/uploads"
 
     - name: Setup docker network
       docker_network:
@@ -221,7 +224,7 @@
           POSTGRES_PASSWORD: "{{ hedgedoc_postgres_password }}"
           POSTGRES_DB: "hedgedoc"
         volumes:
-          - "/srv/data/hedgedoc/data/database:/var/lib/postgresql/data"
+          - "{{ data_dir }}/hedgedoc/data/database:/var/lib/postgresql/data"
         networks:
           - name: hedgedocnet
     
@@ -247,7 +250,7 @@
           CMD_DB_USERNAME: "hedgedoc"
           CMD_DB_PASSWORD: "{{ hedgedoc_postgres_password }}"
         volumes:
-          - /srv/data/hedgedoc/data/uploads:/hedgedoc/public/uploads
+          - "{{ data_dir }}/hedgedoc/data/uploads:/hedgedoc/public/uploads"
         networks:
           - name: hedgedocnet