Maddy tries to use a localhost dns resolver instead of the nameserver specified in /etc/resolve.conf

# Describe the bug

I set up a maddy service on a Vultr VPS, and it seems maddy does not respect the nameserver settings in `/etc/resolve.conf` and tries to read from localhost resolver.
Restart the service solves the problem, but I have to restart the service everytime I reboot.

# Steps to reproduce

1. Setup the systemd service for maddy.
2. Reboot
3. Try to send a mail to a remote host.

# Log files

```
queue: delivery attempt failed {"msg_id":"90b4eed2","rcpt":"rcpt@example.com","reason":"read udp 127.0.0.1:40762-\u003e127.0.0.1:53: read: connection refused","smtp_code":554,"smtp_enchcode":"5.4.4","smtp_msg":"MX lookup error","target":"remote"}
```

# Configuration file

```
$(hostname) = mx.myhost.name
$primary_domain) = myhost.name
$(local_domains) = $(primary_domain)
hostname mx.myhost.name
tls file ${cert.directory}/fullchain.pem ${cert.directory}/key.pem

auth.pass_table local_authdb {
table sql_table {
driver sqlite3
dsn credentials.db
table_name passwords
}
}

storage.imapsql local_mailboxes {
driver sqlite3
dsn imapsql.db
}

table.chain local_rewrites {
optional_step regexp "(.+)\+(.+)@(.+)" "$1@$3"
optional_step static {
entry postmaster mlatus@$(primary_domain)
}
optional_step file /etc/maddy/aliases
}

msgpipeline local_routing {
# Insert handling for special-purpose local domains here.
# e.g.
# destination lists.example.org {
# deliver_to lmtp tcp://127.0.0.1:8024
# }

destination postmaster $(local_domains) {
modify {
replace_rcpt &local_rewrites
}

deliver_to &local_mailboxes
}

default_destination {
reject 550 5.1.1 "User doesn't exist"
}
}

smtp tcp://0.0.0.0:25 {
limits {
# Up to 20 msgs/sec across max. 10 SMTP connections.
all rate 20 1s
all concurrency 10
}

dmarc yes
check {
require_mx_record
dkim
spf
}

source $(local_domains) {
reject 501 5.1.8 "Use Submission for outgoing SMTP"
}
default_source {
destination postmaster $(local_domains) {
deliver_to &local_routing
}
default_destination {
reject 550 5.1.1 "User doesn't exist"
}
}
}

submission tls://0.0.0.0:465 tcp://0.0.0.0:587 {
limits {
# Up to 50 msgs/sec across any amount of SMTP connections.
all rate 50 1s
}

auth &local_authdb

source $(local_domains) {
check {
authorize_sender {
prepare_email &local_rewrites
user_to_email identity
}
}

destination postmaster $(local_domains) {
deliver_to &local_routing
}
default_destination {
modify {
dkim $(primary_domain) $(local_domains) default
}
deliver_to &remote_queue
}
}
default_source {
reject 501 5.1.8 "Non-local sender domain"
}
}

target.remote outbound_delivery {
limits {
# Up to 20 msgs/sec across max. 10 SMTP connections
# for each recipient domain.
destination rate 20 1s
destination concurrency 10
}
mx_auth {
dane
mtasts {
cache fs
fs_dir mtasts_cache/
}
local_policy {
min_tls_level encrypted
min_mx_level none
}
}
}

target.queue remote_queue {
target &outbound_delivery

autogenerated_msg_domain $(primary_domain)
bounce {
destination postmaster $(local_domains) {
deliver_to &local_routing
}
default_destination {
reject 550 5.0.0 "Refusing to send DSNs to non-local addresses"
}
}
}

imap tls://0.0.0.0:993 tcp://0.0.0.0:143 {
auth &local_authdb
storage &local_mailboxes
}
```

# Environment information

* maddy version: 0.5.4

Start by examining how the systemd service initializes DNS resolution and how that differs before and after reboot. Compare the resolver used by maddy with the nameserver in /etc/resolve.conf; done means remote MX lookups work after reboot without restarting the service.

Written by the indexing model from the issue text.