Override the default Dependabot configuration for npm (used by /example/test_harness/).

Reaction to #453

I need to do this in order to prevent Dependabot from creating a `dependencies` label in this repository every time it creates a PR.

The `directory` and `schedule.interval` options are required and it doesn't look like it's possible to tell them to inherit the defaults.
This is why I have had to explicitly give them values here.
In turn I've upgraded from 'daily' to 'weekly' for interval as that feels more appropriately prompt.

see: https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#configuration-options-for-the-dependabotyml-file

Author: QuintinWillison

.github/dependabot.yml

@@ -0,0 +1,7 @@
+version: 2
+updates:
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "daily" # weekdays (Monday to Friday)
+    labels: [ ] # prevent the default `dependencies` label from being added to pull requests