dns: T5959: Streamline dns forwarding service

Streamline configuration and operation of dns forwarding service in
following ways:

- Remove `dns_forwarding_reset.py` as its functionality is now covered
  by `dns.py`
- Adjust function names in `dns.py` to disambiguate between DNS
  forwarding and dynamic DNS
- Remove `dns_forwarding_restart.sh` as its functionality is inlined in
  `dns-forwarding.xml`
- Templatize systemd override for `pdns-recursor.service` and move the
  generated override files in /run. This ensures that the override files
  are always generated afresh after boot
- Simplify the systemd override file by removing the redundant overrides
- Relocate configuration path for pdns-recursor to `/run/pdns-recursor`
  and utilize the `RuntimeDirectory` default that pdns-recursor expects
- We do not need to use custom `--socket-dir` path anymore, the default
  path (viz., `/run/pdns-recursor` is fine)

1 files changed, 8 insertions, 0 deletions

diff --git a/data/templates/dns-forwarding/override.conf.j2 b/data/templates/dns-forwarding/override.conf.j2
new file mode 100644
index 000000000..9d81a2977
--- /dev/null
+++ b/data/templates/dns-forwarding/override.conf.j2
@@ -0,0 +1,8 @@
+[Unit]
+ConditionPathExists={{ config_file }}
+After=vyos-router.service
+
+[Service]
+RuntimeDirectoryPreserve=yes
+ExecStart=
+ExecStart=/usr/sbin/pdns_recursor --daemon=no --write-pid=no --disable-syslog --log-timestamp=no --config-dir={{ config_dir }}