ci: Add the label-check workflow to verify changelog labels on each PR (

#4847)

## Which problem is this PR solving?
- part of: #4799
- [x] Add a GitHub Action that will verify that a PR has a specific
categorization label before it can be merged. We already have a bunch of
those labels changelog:*** labels

## Description of the changes
- This workflow would first check if the PR is created by @dependabot or
not. If no, it would proceed to check for the labels on that pull
request. For example:
- A new PR is created. The Label Check workflow would fail
- A maintainer adds some label `bug` on the PR, workflow would again
run, but would still fail since the label `bug` doesn't start with
`changelog:`
- The maintainer now adds some label `changelog:**`, this time, Label
Check CI would pass.

## How was this change tested?
- Without any label, failed GH Action:
https://github.com/anshgoyalevil/jaeger/actions/runs/6531596646/attempts/2
- With the Label `changelog: feature`: Passing GH Action:
https://github.com/anshgoyalevil/jaeger/actions/runs/6531596646/attempts/3
- With the label `bug` and not `changelog: feature`:
https://github.com/anshgoyalevil/jaeger/actions/runs/6531596646/attempts/4
- With three labels `bug`, `documentation`, and `changelog: feature`:
https://github.com/anshgoyalevil/jaeger/actions/runs/6531596646

## How to test this PR?
- Play with the labels by applying or removing them and see the Verify
Label action fail/pass.

## Checklist
- [x] I have read
https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
- [x] I have signed all commits
- [x] I have added unit tests for the new functionality
- [x] I have run lint and test steps successfully
  - for `jaeger`: `make lint test`
  - for `jaeger-ui`: `yarn lint` and `yarn test`.

---------

Signed-off-by: Ansh Goyal <anshgoyal1704@gmail.com>
Co-authored-by: Yuri Shkuro <yurishkuro@users.noreply.github.com>

.github/workflows/ci-label-check.yml

@@ -0,0 +1,30 @@
+name: Verify PR Label
+
+on:
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - ready_for_review
+      - labeled
+      - unlabeled
+
+jobs:
+  check-label:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check PR author
+        id: check_author
+        run: echo "::set-output name=is_dependabot::$(echo ${{ github.event.pull_request.user.login }} | grep -o 'dependabot')"
+
+      - name: Check PR label
+        if: steps.check_author.outputs.is_dependabot != 'dependabot'
+        run: |
+          LABEL_NAME="changelog:"
+          if [[ $(curl -s "https://api.github.com/repos/${{ github.repository }}/pulls/${{ github.event.pull_request.number }}" | jq -r '.labels[].name' | grep -c "^$LABEL_NAME") -eq 0 ]]; then
+            echo "Error: Pull request is missing a required label of the form '${LABEL_NAME}***'."
+            exit 1
+          fi
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}