General 9.5 release checklist

- [x] Bump version
- `:vimgrep '\(\<9\.\?4\>\)\|\(94_\)' **/*.rst *.py`
- [x] Update all installation steps to use new package name
- [x] Update our upgrade steps
- [x] Verify Installation steps with new packages (single-machine cluster install)
- [x] Debian 8 Jessie — ami-0e79236b
- requires https://unix.stackexchange.com/a/508728
- [x] Debian 9 Stretch — ami-066a93633945763a8
- [x] Debian 10 Buster — ami-0ea08f325bd2bbf69
- [x] Ubuntu 16.04 Xenial — ami-0765f2a0e038358f8
- [x] Ubuntu 18.04 Bionic Beaver — ami-0ee5e851705bfaf7a
- [x] Ubuntu 20.04 Focal — ami-0cfc8da67f8bd8679
- [ ] CentOS 6 — ami-0db8e77c005d79e33
- ERROR: epoll_ctl() failed: No such file or directory
- [x] CentOS 7 — ami-01e36b7901e884a10
- [x] CentOS 8 — ami-04703ea1a1d8f892f
- [ ] RHEL 6 — ami-02d0e2f9af142f67e
- ERROR: epoll_ctl() failed: No such file or directory
- [x] RHEL 7 — ami-015d91fd7a96cbfbd
- [x] RHEL 8 — ami-00c1b07c4c4322ad4
- [x] Test Multi-tenant tutorial and use-case guide (on just one version)
- [x] Test Real-time analytics tutorial and use-case guide (on Docker)
- [x] scan for any other udf and guc changes (in Community and Enterprise)
- Did this already in a separate task for 9.5
- [x] Scan for updated extensions on Citus Cloud
- [x] Verify there are no Sphinx warnings in local build
- `sphinx-build -b html -a -n -W . _build`
- (Remove _build directory and try fresh too)
- [ ] Test enterprise install on one debian and one centos version
- postgresql-12-citus-enterprise-9.5 is not yet released
- [x] Update citusdata.com/download links.
- [ ] Confirm with Claire that it goes live after merge
- [x] Create new 9.5 release branch and set as default ver in RTD (advanced settings tab)
- [x] Rebuild previous version so that canonical link gets updated

Review the remaining unchecked checklist items, especially CentOS 6 and RHEL 6 installation failures, enterprise installation, and confirmation of the download links. Start by checking the documented installation environments and run the listed sphinx-build command; done means the outstanding release checks are resolved or explicitly documented.

Written by the indexing model from the issue text.