Add a style-check workflow

Add a CI job that evaluates style issues, restricted only to lines
changed for the affected files in a given commit

Also provide a mechanism to waive those style issues.  by applying the
style:exempted label to a PR, the checks are still run (its nice to see
what they are regardless), but the test will pass CI regardless of
weather any issues are found.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
(Merged from https://github.com/openssl/openssl/pull/24806)

.github/workflows/style-checks.yml

@@ -0,0 +1,55 @@
+# Copyright 2021-2024 The OpenSSL Project Authors. All Rights Reserved.
+#
+# Licensed under the Apache License 2.0 (the "License").  You may not use
+# this file except in compliance with the License.  You can obtain a copy
+# in the file LICENSE in the source distribution or at
+# https://www.openssl.org/source/license.html
+
+name: Coding style validation 
+
+on: [pull_request]
+
+env:
+  PR_NUMBER: ${{ github.event.number }}
+  GH_TOKEN: ${{ github.token }}
+
+permissions:
+  contents: read
+
+jobs:
+  check-style:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+        path: openssl
+    - name: check style for each commit 
+      working-directory: openssl
+      shell: bash
+      run: |
+        ERRORS_FOUND=0
+        git fetch origin $GITHUB_BASE_REF:$GITHUB_BASE_REF
+        REFSTART=$(git rev-parse $GITHUB_BASE_REF)
+        REFEND=$(git rev-parse HEAD)
+        echo "Checking from $REFSTART to $REFEND"
+        for i in $(git log --no-merges --format=%H $REFSTART..$REFEND)
+        do
+          echo "::group::Style report for commit $i"
+          set +e
+          ./util/check-format-commit.sh $i
+          if [ $? -ne 0 ]
+          then
+            ERRORS_FOUND=1
+          fi
+          set -e
+          echo "::endgroup::"
+        done
+        SKIP_TEST=$(gh pr view $PR_NUMBER --json labels --jq '.labels[] | select(.name == "style: waived") | .name')
+        if [ -z "$SKIP_TEST" ]
+        then
+          exit $ERRORS_FOUND
+        else
+          echo "PR $PR_NUMBER is marked with style: waived, waiving style check errors"
+          exit 0
+        fi