Automate more of the Python upgrade #319

When a new python version is released we currently have the checklist in https://github.com/DiamondLightSource/python-copier-template/blob/main/.github/workflows/new_python.yml. Many of these steps could be done automatically by renovate e.g. something like:

{
  "regexManagers": [
    {
      "fileMatch": ["^\\.github/workflows/.*\\.ya?ml$"],
      "matchStrings": [
        "python-version:\\s*\

\[(?<currentVersions>[^\\]

]+)\\]

"
      ],
      "datasourceTemplate": "python",
      "depNameTemplate": "python",
      "versioningTemplate": "pep440"
    }
  ]
}

in the renovate.json should update the versions under test.

There are probably differing opinions of how much of this we do automatically, semi-automatically or manually based on risk. My preference would be to split the move into two steps:

• Adding the new version as supported - e.g. adding it to the versions under test and to the classifiers. I would say if the tests pass then merge this w/o human input
• Deprecating the old one. I think this does need human intervention as it's risky and there may be valid reasons it's hard. However, we can probably still get renovate to make the PR for it.

Acceptance Criteria

• We decide how much of the process should be automated
• The decision is written in https://diamondlightsource.github.io/python-copier-template/main/explanations/decisions/0022-spec-0.html
• We automate the agreed upon steps (or make a new issue if hard)