Publinker domain-connect template (#571)

# Description

This template enables our customers to verify their domains on Google in
an easier way (without the need of handling API calls)

## Type of change

Please mark options that are relevant.

- [X] New template
- [ ] 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
- [X] Schema validated using JSON Schema
[template.schema](./template.schema)
- [X] Template functionality checked using [Online
Editor](https://pdnsadmin.revproxy.short-lived.de/dc/free/templateedit)
- [X] Template is checked using [template
linter](https://github.com/Domain-Connect/dc-template-linter)
- [X] Template file name follows the pattern
`<providerId>.<serviceId>.json`

# Example variable values
<-- to make review process easier please provide example set of variable
values for this template -->

<-- Example: -->

```
verifytxt: google-site-verification=hxxy5AFS-tpVUIEXEghO8GCtGj45f7LX30D6qxKdkYM
```

<-- Or provide the whole `testData` object from the [Online
Editor](https://pdnsadmin.revproxy.short-lived.de/dc/free/templateedit)
after testing and using "Add as test" button -->
```
"testData": {
    "publinker.com.google-domain-verification.json": {
      "variables": {
        "domain": "example.com",
        "verifytxt": "google-site-verification=hxxy5AFS-tpVUIEXEghO8GCtGj45f7LX30D6qxKdkYM"
      },
      "results": [
        {
          "type": "TXT",
          "name": "@",
          "ttl": 3600,
          "data": "\"google-site-verification=hxxy5AFS-tpVUIEXEghO8GCtGj45f7LX30D6qxKdkYM\""
        }
      ]
    }
  }
```

publinker.com.google-domain-verification.json

@@ -0,0 +1,23 @@
+{
+    "providerId": "publinker.com",
+    "providerName": "Publinker",
+    "serviceId": "google-domain-verification",
+    "serviceName": "Google Domain Verification",
+    "sharedServiceName": true,
+    "version": 1,
+    "logoUrl": "https://publinker.com/assets/logo/publinker-low-resolution-logo-color-on-transparent-background.png",
+    "description": "Enables a domain to be authorized and verified by Google",
+    "variableDescription": "Unique verification code provided by Google for purpose of verification",
+    "multiInstance": true,
+    "syncBlock": false,
+    "syncPubKeyDomain": "publinker.com",
+    "records": [
+        {
+            "groupId": "verification",
+            "type": "TXT",
+            "host": "@",
+            "data": "%verifytxt%",
+            "ttl": 3600
+        }
+    ]
+}