Add Source Internal IP selector (cloudflare#26668)

Author: maxvp

src/content/docs/cloudflare-one/traffic-policies/dns-policies/index.mdx

@@ -450,6 +450,14 @@ Use this selector to filter based on the country where the query arrived to Gate
 
 <Render file="gateway/selectors/source-ip-resolver" product="cloudflare-one" />
 
+### Source Internal IP
+
+Use this selector to apply policies to the source internal IP address of a DNS query. For example, this could be the private IP address of the hosts behind [Magic WAN](/magic-wan/zero-trust/cloudflare-gateway/) or [WARP Connector](/cloudflare-one/networks/connectors/cloudflare-tunnel/private-net/warp-connector/) used by your organization to send queries to Gateway.
+
+| UI name            | API example                        | Evaluation phase      |
+| ------------------ | ---------------------------------- | --------------------- |
+| Source Internal IP | `dns.src_internal_ip == 10.10.0.1` | Before DNS resolution |
+
 ### Users
 
 <Render file="gateway/selectors/users-dns" product="cloudflare-one" />