r/protonvpn: Move remote_addrs file to /var

If `/` is mounted read-only, as is usually the case, the Proton VPN
watchdog cannot update the `remote_addrs` configuration file.  It needs
to be stored in a directory that is guaranteed to be writable.

roles/protonvpn/files/protonvpn-watchdog.py

@@ -102,7 +102,7 @@ class AsyncDaemon(BaseAsyncDaemon):
     )
     CONFIG = os.environ.get(
         'PROTONVPN_CONFIG',
-        '/etc/strongswan/swanctl/conf.d/protonvpn.remote_addrs',
+        '/var/lib/protonvpn/remote_addrs',
     )
 
     def __init__(self) -> None:
@@ -215,6 +215,8 @@ class AsyncDaemon(BaseAsyncDaemon):
         if not self.serverlist:
             log.error('Cannot reconfigure: no known servers!')
             return
+        if not os.path.isdir(os.path.dirname(self.CONFIG)):
+            os.makedirs(os.path.dirname(self.CONFIG))
         fd = os.open(self.CONFIG, os.O_CREAT | os.O_RDWR, 0o644)
         with open(fd, 'r+', encoding='utf-8') as f:
             line = f.readline()