chore: disable dependabot on login (#10265)

# Which Problems Are Solved

- Dependabot creates noisy PRs to the mirror repo zitadel/typescript.

# How the Problems Are Solved

- We mark the dependabot file as an example, effectively disabling
dependabot.
- For cases this isn't intuitive enough, we add a guiding sentence to
the README.md
- Dependabot for the login [is already enabled in the zitadel
repo](https://github.com/zitadel/zitadel/blob/main/.github/dependabot.yml#L25-L37).

# Additional Changes

- Updates the CONTRIBUTING.md with instructions about how to submit
changes related to the mirror repo.
- @stebenz please dismiss the relevant Vanta checks if necessary.

---------

Co-authored-by: Copilot <[email protected]>

login/.github/dependabot.example.yml

@@ -0,0 +1,21 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: '/'
+    open-pull-requests-limit: 1
+    schedule:
+      interval: 'daily'
+
+  - package-ecosystem: npm
+    directory: '/'
+    open-pull-requests-limit: 3
+    schedule:
+      interval: daily
+    groups:
+      prod:
+        dependency-type: production
+      dev:
+        dependency-type: development
+    ignore:
+      - dependency-name: "eslint"
+        versions: [ "9.x" ]