feat(dns): DNS_UPSTREAM_RESOLVER_TYPE option which can be plain or DoT

- Migrate `DOT` to `DNS_SERVER`
- Migrate `DOT_PROVIDERS` to `DNS_UPSTREAM_RESOLVERS`
- Migrate `DOT_PRIVATE_ADDRESS` to `DNS_PRIVATE_ADDRESSES`
- Migrate `DOT_CACHING` to `DNS_CACHING`
- Migrate `DOT_IPV6` to `DNS_UPSTREAM_IPV6`

internal/configuration/settings/settings_test.go

@@ -40,12 +40,13 @@ func Test_Settings_String(t *testing.T) {
 ├── DNS settings:
 |   ├── Keep existing nameserver(s): no
 |   ├── DNS server address to use: 127.0.0.1
-|   ├── DNS over TLS forwarder enabled: yes
-|   ├── Update period: every 24h0m0s
+|   ├── DNS forwarder server enabled: yes
+|   ├── Upstream resolver type: dot
 |   ├── Upstream resolvers:
 |   |   └── Cloudflare
 |   ├── Caching: yes
 |   ├── IPv6: no
+|   ├── Update period: every 24h0m0s
 |   └── DNS filtering settings:
 |       ├── Block malicious: yes
 |       ├── Block ads: no