feat(custom): add custom provider

- Sends HTTP GET request to url given with ip information
- Configurable ipv4 and ipv6 query parameter keys
- Configurable response success detection with a regex
- Treat non status OK 200 responses as failures

docs/custom.md

@@ -0,0 +1,40 @@
+# Custom provider
+
+The custom provider allows to configure a URL with a few additional parameters to update your records.
+
+For now it sends an HTTP GET request to the URL given with some additional parameters.
+Feel free to open issues to extend its configuration options.
+
+## Configuration
+
+### Example
+
+```json
+{
+  "settings": [
+    {
+      "provider": "custom",
+      "domain": "example.com",
+      "host": "@",
+      "url": "https://example.com/update?domain=example.com&host=@&username=username&client_key=client_key",
+      "ipv4key": "ipv4",
+      "ipv6key": "ipv6",
+      "success_regex": "good",
+      "ip_version": "ipv4"
+    }
+  ]
+}
+```
+
+### Compulsory parameters
+
+- `"domain"` is the domain name to update
+- `"host"` is the host to update, which can be `"@"` (root), `"*"` or a subdomain
+- `"url"` is the URL to update your records and should contain all the information EXCEPT the IP address to update
+- `"ipv4key"` is the URL query parameter name for the IPv4 address, for example `ipv4` will be added to the URL with `&ipv4=1.2.3.4`.
+- `"ipv6key"` is the URL query parameter name for the IPv6 address, for example `ipv6` will be added to the URL with `&ipv6=::aaff`. Even if you don't use IPv6, this must be set to something.
+- `"success_regex"` is a regular expression to match the response from the server to determine if the update was successful. You can use [regex101.com](https://regex101.com/) to find the regular expression you want. For example `good` would match any response containing the word "good".
+
+### Optional parameters
+
+- `"ip_version"` can be `ipv4` (A records) or `ipv6` (AAAA records), defaults to `ipv4 or ipv6`