Add helper script to extract and reformat release notes

[mozzieongit]

@wtoorop I wrote a bash script for what we talked about ^^

It can extract the release notes for the latest or specified version, generate the email (including the checksum, if the file exists), and convert to the YAML format for the website.

Examples:

$ ./convert-release-notes.sh 4.12.0
4.12.0
================
FEATURES:
- Merge #418: Support for DSYNC, EID, NIMLOC, SINK, TALINK, DOA,
  AMTRELAY and IPN resource record types.
- Merge #420: Zones get state "old-serial" with
  `nsd-control zonestatus` when the served serial is older than
  the one received by the transfer daemon.
- Merge #429: Add prometheus metrics

BUG FIXES:
- Fix re-enable to configure dns-cookies from config file, which was
  accidentally removed with the 4.11.1 release.
...
- Fix to update common.sh for speed of kill_pid.
- Fix nsd-checkzone ixfr create cleanup on exit.

$ ./convert-release-notes.sh -y 4.12.0
---
version: 4.12.0
date: 24 April, 2025
features:
- >-
  Merge #418: Support for DSYNC, EID, NIMLOC, SINK, TALINK, DOA,
  AMTRELAY and IPN resource record types.
- >-
  Merge #420: Zones get state "old-serial" with                         
  `nsd-control zonestatus` when the served serial is older than         
  the one received by the transfer daemon.
- >-
  Merge #429: Add prometheus metrics
bugs:
- >-
  Fix re-enable to configure dns-cookies from config file, which was
  accidentally removed with the 4.11.1 release.
- >-
  Fix #426: nsd crashes with patterns in config_apply_pattern.
...
- >-
  Fix nsd-checkzone ixfr create cleanup on exit.