breaking(env): change _base to $shared

Change `_base` to `$shared` and `DEFAULT_HEADERS` to
`$default_headers`.

docs/docs/usage/dotenv-and-http-client.env.json-support.md

@@ -90,15 +90,16 @@ Authorization: Bearer {{API_KEY}}
 
 You can define default HTTP headers in the `http-client.env.json` file.
 
-You need to put them in the special `_base` property and
-the `DEFAULT_HEADERS` will be merged with the headers from the HTTP requests.
+You need to put them in the special `$shared` property and
+the `$default_headers` will be merged with the headers from the HTTP requests.
 
 ```json title="http-client.env.json"
 {
-  "_base": {
-    "DEFAULT_HEADERS": {
+  "$shared": {
+    "$default_headers": {
       "Content-Type": "application/json",
       "Accept": "application/json"
+    },
   },
   "dev": {
     "API_KEY": "your-api-key"

lua/kulala/parser/env.lua

@@ -68,16 +68,17 @@ M.get_env = function()
 
   if http_client_env_json then
     local f = vim.fn.json_decode(vim.fn.readfile(http_client_env_json))
-    if f._base then
-      DB.update().http_client_env_base = vim.tbl_deep_extend("force", DB.find_unique("http_client_env_base"), f._base)
+    if f["$shared"] then
+      DB.update().http_client_env_base =
+        vim.tbl_deep_extend("force", DB.find_unique("http_client_env_base"), f["$shared"])
     end
-    f._base = nil
+    f["$shared"] = nil
     DB.update().http_client_env = vim.tbl_deep_extend("force", DB.find_unique("http_client_env"), f)
   end
 
   local http_client_env_base = DB.find_unique("http_client_env_base") or {}
   for key, value in pairs(http_client_env_base) do
-    if key ~= "DEFAULT_HEADERS" then
+    if key ~= "$default_headers" then
       env[key] = value
     end
   end

schemas/http-client.env.json

@@ -6,6 +6,26 @@
   "properties": {
     "$schema": {
       "type": "string"
+    },
+    "$shared": {
+      "type": "object",
+      "properties": {
+        "$default_headers": {
+          "type": "object",
+          "patternProperties": {
+            "^.*$": {
+              "type": "string"
+            }
+          },
+          "additionalProperties": false
+        }
+      },
+      "patternProperties": {
+        "^.*$": {
+          "type": "string"
+        }
+      },
+      "additionalProperties": false
     }
   },
   "patternProperties": {