docs: add release notes for 4.9 to documentation

[keithf4]

Description

Add release notes for 4.9 to official docs

Please indicate what kind of change your PR includes (multiple selections are acceptable):

• [ ] Bugfix
• [ ] Enhancement
• [ ] Breaking Change
• [x] Documentation

Testing

None of the testing listed below is optional.

• Installation method:
  • [ ] Binary install from source, version:
  • [ ] OS package repository, distro, and version:
  • [ ] Local package server, version:
  • [ ] Custom-built package, version:
  • [ ] Other:
• [ ] PostgreSQL, Specify version(s):
• [x] docs tested with hugo version(s): v0.80.0/extended

Code testing

Have you tested your changes against:

• [ ] RedHat/CentOS
• [ ] Ubuntu
• [ ] SLES
• [x] Not applicable

If your code touches postgres_exporter, have you:

• [ ] Tested against all versions of PostgreSQL affected
• [ ] Ensure that exporter runs with no scrape errors
• [x] Not applicable

If your code touches node_exporter, have you:

• [ ] Ensure that exporter runs with no scrape errors
• [x] Not applicable

If your code touches Prometheus, have you:

• [ ] Ensured all configuration changes pass promtool check config
• [ ] Ensured all alert rule changes pass promtool check rules
• [ ] Prometheus runs without issue
• [ ] Alertmanager runs without issue
• [x] Not applicable

If your code touches Grafana, have you:

• [ ] Ensured Grafana runs without issue
• [ ] Ensured relevant dashboards load without issue
• [x] Not applicable

Checklist:

• I have made corresponding changes to:
  • [ ] the documentation
  • [ ] the release notes
  • [ ] the upgrade doc

[jchancojr]

lgtm unless we want bouncer named consistently as pgBouncer. otherwise 👍

[keithf4]

lgtm unless we want bouncer named consistently as pgBouncer. otherwise 👍

Fixed consistency for it in most recent version notes. Made it like it is in HA