Add `source` configuration option

Remove unused configuration options provided by layer.

src/config.yaml

@@ -0,0 +1,23 @@
+options:
+  source:
+    default: distro
+    type: string
+    description: |
+      Repository from which to install OVS+OVN
+
+      May be one of the following:
+
+        distro (default)
+        ppa:somecustom/ppa (PPA name must include UCA OpenStack Release name)
+        deb url sources entry|key id
+        or a supported Ubuntu Cloud Archive pocket.
+
+      Supported Ubuntu Cloud Archive pockets include:
+
+        cloud:xenial-pike
+        cloud:xenial-queens
+        cloud:bionic-rocky
+
+      Note that updating this setting to a source that is known to
+      provide a later version of Ceph will trigger a software
+      upgrade.

src/layer.yaml

@@ -9,4 +9,10 @@ options:
 repo: https://github.com/openstack/charm-ovn-controller
 config:
   deletes:
+    - debug
+    - ssl_ca
+    - ssl_cert
+    - ssl_key
+    - use-internal-endpoints
+    - use-syslog
     - verbose

src/lib/charm/openstack/ovn_chassis.py

@@ -52,6 +52,7 @@ class OVNChassisCharm(charms_openstack.charm.OpenStackCharm):
         '/etc/default/ovn-host': ['ovn-host'],
     }
     python_version = 3
+    source_config_key = 'source'
     # Name of unitdata key with information on whether to enable metadata
     metadata_kv_key = 'ovn-chassis-enable-metadata'