fix: resend host domain key (#575)

# Description

Fix an issue where the domain key was using the wrong host value.

## Type of change

Please mark options that are relevant.

- [ ] New template
- [x] Bug fix (non-breaking change which fixes an issue in the template)
- [ ] New feature (non-breaking change which adds functionality to the
template)
- [ ] Breaking change (fix or feature that would cause existing template
behavior to be not backward compatible)

# How Has This Been Tested?

Please mark the following checks done
- [ ] Schema validated using JSON Schema
[template.schema](./template.schema)
- [ ] Template functionality checked using [Online
Editor](https://domainconnect.paulonet.eu/dc/free/templateedit)
- [ ] Template is checked using [template
linter](https://github.com/Domain-Connect/dc-template-linter)
- [ ] Template file name follows the pattern
`<providerId>.<serviceId>.json`

# Example variable values

```
region: us-east-1
publicKey: RANDOM-VALUE
```

resend.com.mail.json

@@ -3,7 +3,7 @@
 	"providerName": "Resend",
 	"serviceId": "mail",
 	"serviceName": "Mail",
-	"version": 1,
+	"version": 2,
 	"syncPubKeyDomain": "resend.com",
 	"syncRedirectDomain": "resend.com",
 	"description": "Enable email signing and specify authorized senders.",
@@ -24,7 +24,7 @@
 		},
 		{
 			"type": "TXT",
-			"host": "send",
+			"host": "resend._domainkey",
 			"ttl": 3600,
 			"data": "p=%domainKey%"
 		}