Added exec summary to changelog, misc other small fixes/corrections. (#5845)

* Pull Release/snapshot description from Executive Summary of
CHANGELOG.md.

* Change bullets to h3 headings (###)

.github/workflows/release-files.yml

@@ -208,15 +208,9 @@ jobs:
         run: |
           echo "${{ steps.get-file-base.outputs.FILE_BASE }}" > ./last-file.txt
 
-      - name: Get NEWSLETTER
-        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4.3.0
-        with:
-              name: NEWSLETTER
-              path: ${{ github.workspace }}
-
-      - name: Create description file
+      - name: Create description for release/snapshot from "Executive Summary" section of CHANGELOG.md
         run: |
-          cat ${{ github.workspace }}/NEWSLETTER.txt > description.txt
+          sed -n '/^# .* Executive Summary: HDF5 Version .*/,/^# .* Breaking Changes/p' CHANGELOG.md | sed '$d' > description.txt
 
       - name: PreRelease tag
         id: create_prerelease