fix(ci): remove Dependabot config and minor Renovate config update (#1920)

This PR removes Dependabot config (as we use Renovate) and updates
Renovate config with weekly schedule for `cargo` packages upgrade.

### Checklist
<!-- Put an 'x' in all the boxes that apply -->
- [ ] I have added tests to cover my changes or documented any manual
tests.
- [ ] I have updated the
[documentation](https://github.com/open-edge-platform/datumaro/tree/develop/docs)
accordingly

Signed-off-by: Barabanov <[email protected]>

Author: AlexanderBarabanov

.github/dependabot.yml

@@ -50,6 +50,12 @@
       matchManagers: ["pip_requirements"],
     },
 
+    {
+      enabled: true,
+      matchManagers: ["cargo"],
+      schedule: ["* * * * 0"], // weekly
+    },
+
     // Disable derive_more major upgrades to prevent regressions
     // Will be enabled in a next step
     {