chore(loki): dependabot enhancements (#10025)

**What this PR does / why we need it**:
This introduces following changes
1. change open-pull-requests-limit from 2 -> 5 for root level go.mod
dependencies
2. Add dependabot also other go.mod files in `/operator`.
3. Add dependabot tracking for docker images under `/cmd/loki/`


**Which issue(s) this PR fixes**:
Fixes #<issue number>

**Special notes for your reviewer**:
NOTES:
1. [There is go.mod cleanup PR open
](#10023) that make most some
internal tools to use just one `go.mod` at the root level.
2. Will add tracking to other docker images in other directories in
follow up PR

**Checklist**
- [x] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)

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

.github/dependabot.yml

@@ -1,11 +1,26 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
 version: 2
 updates:
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
       interval: "weekly"
+    open-pull-requests-limit: 5
   - package-ecosystem: "gomod"
     directory: "/"
     schedule:
       interval: "daily"
-    open-pull-requests-limit: 2
+    open-pull-requests-limit: 5
+  - package-ecosystem: "gomod"
+    directory: "/operator"
+    schedule:
+      interval: "daily"
+    open-pull-requests-limit: 5
+  - package-ecosystem: docker
+    directory: /cmd/loki
+    schedule:
+      interval: "daily"