feat(debian): add bullseye support

PR progress checklist (to be filled in by reviewers)

[ ] Changes to documentation are appropriate (or tick if not required)
[ ] Changes to tests are appropriate (or tick if not required)
[ ] Reviews completed

What type of PR is this?

Primary type

[ ] [build] Changes related to the build system
[ ] [chore] Changes to the build process or auxiliary tools and libraries such as documentation generation
[ ] [ci] Changes to the continuous integration configuration
[x] [feat] A new feature
[ ] [fix] A bug fix
[ ] [perf] A code change that improves performance
[ ] [refactor] A code change that neither fixes a bug nor adds a feature
[ ] [revert] A change used to revert a previous commit
[ ] [style] Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc.)

Secondary type

[ ] [docs] Documentation changes
[ ] [test] Adding missing or correcting existing tests

Does this PR introduce a `BREAKING CHANGE`?

No.

Related issues and/or pull requests

N/A. No one has documented an attempt to run this formula on debian bullseye (testing) at this stage.

Describe the changes you're proposing

Hi there. Currently, installation on debian bullseye results in a broken APT configuration if use_upstream_repo is set to True. The string "postgresql-repo" string is entered into the /etc/apt/sources.list.d/pgdg.list file. This results in apt being unusable in the target system, which ideally should not happen.

My changes resolve this issue by adding support for debian bullseye (testing)

Pillar / config required to test the proposed changes

postgres:
  use_upstream_repo: True
  fromrepo: bullseye-pgdg
  version: '13'

Debug log showing how the proposed changes work

root@saltmain:/srv/formulas# salt 'unicornbottle-main' state.apply postgres.upstream
unicornbottle-main:
  Name: postgresql-pkg-deps - Function: pkg.installed - Result: Clean Started: - 15:21:26.534113 Duration: 23.875 ms
  Name: deb http://apt.postgresql.org/pub/repos/apt bullseye-pgdg main - Function: pkgrepo.managed - Result: Changed Started: - 15:21:26.559226 Duration: 6556.887 ms

Summary for unicornbottle-main
------------
Succeeded: 2 (changed=1)
Failed:    0
------------
Total states run:     2
Total run time:   6.581 s

Now configuration is set as follows:

# cat /etc/apt/sources.list.d/pgdg.list
deb http://apt.postgresql.org/pub/repos/apt bullseye-pgdg main

Documentation checklist

[ ] Updated the README (e.g. Available states).
[ ] Updated pillar.example.

Testing checklist

[ ] Included in Kitchen (i.e. under state_top).
[x] Covered by new/existing tests (e.g. InSpec, Serverspec, etc.).
[ ] Updated the relevant test pillar.

Additional context

This is debian's unstable branch. I'm personally using it to be a little more up to date as stability is not a concern for my current project. If I have any issues I'll update here with additional fixes, however I think that how the project is laid out everything should continue to work as this is a very small change which should not have many repercussions.

saltstack-formulas / postgres-formula