Allow postUpgradeTasks for gitea/helm-chart repo (#270)

https://gitea.com/gitea/helm-chart/pulls/734 showed that we have to update the project `README.md` while renovating `values.yaml`.

This configures Renovate to allow running specific commands during branch creation/updates while processing repositories[^1].
Since gitea/helm-chart depends on node.js and npm to update the README, we need to allow installing that tool AND allow the `make` command for actually updating the README.

In preparation of this being merged, https://gitea.com/gitea/helm-chart/pulls/738 configured the usage of these commands.

[^1]: https://docs.renovatebot.com/self-hosted-configuration/#allowedpostupgradecommands for Renovate hosting configuration and https://docs.renovatebot.com/configuration-options/#postupgradetasks for repository configuration.

Signed-off-by: justusbunsi <sk.bunsenbrenner@gmail.com>

Reviewed-on: https://gitea.com/gitea/renovate-config/pulls/270
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.com>
Co-authored-by: justusbunsi <sk.bunsenbrenner@gmail.com>
Co-committed-by: justusbunsi <sk.bunsenbrenner@gmail.com>

config.js

@@ -15,5 +15,10 @@ module.exports = {
             "username": process.env.HUB_DOCKER_COM_USER,
             "password": process.env.HUB_DOCKER_COM_TOKEN
         }
+    ],
+    "allowedPostUpgradeCommands": [
+        // [gitea/helm-chart] Update README.md on dependency changes in values.yaml
+        "install-tool node",
+        "make readme"
     ]
 };