SQSCANGHA-149 Add scannerBinariesAuthHeader input for authenticated binary downloads

Organisations using private Artifactory mirrors require authentication to
download the SonarScanner CLI. This adds an optional scannerBinariesAuthHeader
input whose value is forwarded as the Authorization HTTP header to both the
binary and GPG signature downloads via tc.downloadTool's built-in auth
parameter. No new dependencies are introduced.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

action.yml

@@ -28,6 +28,13 @@ inputs:
     description: Skip GPG signature verification (not recommended for security)
     required: false
     default: "false"
+  scannerBinariesAuthHeader:
+    description: >
+      Authorization header value to use when downloading the SonarScanner CLI binaries
+      (e.g. 'Bearer mytoken' or 'Basic base64creds'). Use this when scannerBinariesUrl
+      points to a private server that requires authentication.
+    required: false
+    default: ""
 runs:
   using: node24
   main: dist/index.js