Create Jaeger override (#602)

Allow customer admins to easily enable Jaeger by adding another Helm values override file to their Helm upgrade install command, and to provide an example if they need to enable Jaeger by modifying their existing override file.

### Checklist

- [x] Follow the [manual testing
process](https://github.com/sourcegraph/deploy-sourcegraph-helm/blob/main/TEST.md)
- [ ] Update
[changelog](https://github.com/sourcegraph/deploy-sourcegraph-helm/blob/main/charts/sourcegraph/CHANGELOG.md)
- [ ] Update [Kubernetes update
doc](https://docs.sourcegraph.com/admin/updates/kubernetes)

### Test plan

Manual testing worked swell

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Author: marcleblanc2

charts/sourcegraph/examples/jaeger/override.yaml

@@ -0,0 +1,2 @@
+jaeger:
+  enabled: true