deploy: allow overriding the Azure Function name via a repo variable

This allows overriding the default Azure Function name used for
deploying via setting a repository secret (in Settings>Secrets and
variables).

The name of the Azure Function is treated as a secret because it can be
used to derive the URL of the Azure Function and to attempt to DOS it.

At this point, it is not _actually_ necessary to provide the correct
Azure Function app name here, as we are using a so-called "publish
profile" that overrides the app name.

However, we are about to switch to Role-Based Access Control, where it
very much matters whether the correct name is specified or not.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.github/workflows/deploy.yml

@@ -18,6 +18,6 @@ jobs:
       - uses: actions/checkout@v5
       - uses: Azure/functions-action@v1
         with:
-          app-name: GitGitGadget
+          app-name: ${{ secrets.AZURE_FUNCTION_NAME || 'GitGitGadget' }}
           publish-profile: ${{ secrets.AZURE_FUNCTIONAPP_PUBLISH_PROFILE }}
           respect-funcignore: true