issuer -> authorizationServer refactor (#250359)

* `issuer` -> `authorizationServer` refactor

Also:
* adds `authorizationServerGlobs` to the authentication contribution schema
* removes ugly MCP issuer hack and instead plumbs the authorizationServer down to the new auth providers

extensions/github-authentication/package.json

@@ -35,14 +35,14 @@
       {
         "label": "GitHub",
         "id": "github",
-        "issuerGlobs": [
+        "authorizationServerGlobs": [
           "https://github.com/login/oauth"
         ]
       },
       {
         "label": "GitHub Enterprise Server",
         "id": "github-enterprise",
-        "issuerGlobs": [
+        "authorizationServerGlobs": [
           "*"
         ]
       }