Automate PR selection for changelog during release

[lexnv]

One task of the releasing activities is to obtain the list of closed PRs, to update the changelog file.
This manual task introduces a delay in the release procedure.
Automate this step via a script / one-liner to obtain the required PRs in format
- {pr-name} [{pr-number}]({pr-link})

• Generate release changelog based on commits #465 (Get committed PRs)
• Option to select a custom release range
• Verifiable tags (signed and included in the latest release)
• Group PRs into sections (Blocked by substrate labels reform)

[jsdw]

We have the nice script now, so I'll close this since it's good enough for now :)