feat(schema): add private.env.schema.json

See: https://www.jetbrains.com/help/idea/exploring-http-syntax.html#example-working-with-environment-files

schemas/http-client.private.env.schema.json

@@ -0,0 +1,43 @@
+{
+  "$id": "https://raw.githubusercontent.com/mistweaverco/kulala.nvim/main/schemas/http-client.private.env.schema.json",
+  "title": "HTTP Client Private Environment Variables",
+  "description": "The private environment variables required for the HTTP client",
+  "type": "object",
+  "properties": {
+    "$schema": {
+      "type": "string"
+    },
+    "$shared": {
+      "type": "object",
+      "properties": {
+        "$default_headers": {
+          "type": "object",
+          "patternProperties": {
+            "^.*$": {
+              "type": "string"
+            }
+          },
+          "additionalProperties": false
+        }
+      },
+      "patternProperties": {
+        "^([A-Za-z0-9_]+)$": {
+          "type": ["string", "number"]
+        }
+      },
+      "additionalProperties": false
+    }
+  },
+  "patternProperties": {
+    "^.*$": {
+      "type": "object",
+      "patternProperties": {
+        "^([A-Za-z0-9_]+)$": {
+          "type": ["string", "number"]
+        }
+      },
+      "additionalProperties": false
+    }
+  },
+  "additionalProperties": false
+}