feat: add headers support to HTTP transport schema, use in GitHub PAT variant

- Add optional `headers` field to HTTP transport schema for sending
  custom headers (supports ${input:ID} interpolation)
- GitHub PAT variant now sends `Authorization: Bearer ${input:GITHUB_TOKEN}`

Signed-off-by: Mohammod Al Amin Ashik <maa.ashik00@gmail.com>

Author: its-mash

schemas/server-definition.schema.json

@@ -167,6 +167,11 @@
               "format": "uri",
               "description": "HTTP endpoint URL (supports Streamable HTTP)"
             },
+            "headers": {
+              "type": "object",
+              "additionalProperties": { "type": "string" },
+              "description": "HTTP headers to send with requests (supports ${input:ID} interpolation)"
+            },
             "metadata": {
               "$ref": "#/$defs/metadata"
             }

servers/com.github-mcp-http-pat.json

@@ -12,6 +12,9 @@
   "transport": {
     "type": "http",
     "url": "https://api.githubcopilot.com/mcp/",
+    "headers": {
+      "Authorization": "Bearer ${input:GITHUB_TOKEN}"
+    },
     "metadata": {
       "inputs": [
         {