#102: Add a preset to manage updates to PYTHON_VERSION is CI files

Summary

Adds a preset to keep the PYTHON_VERSION defined in .gitlab-ci.yml files up to date.

Previous Review

There changes were previously made against the preset repo see review comments here.

Checks

• After running a version of this manager against the Lab Allocator repository the logs included the following:

{
  "deps": [
    {
      "depName": "registry.gitlab.developers.cam.ac.uk/uis/devops/infra/dockerimages/python",
      "currentValue": "3.11",
      "datasource": "docker",
      "depType": "python-version-ci",
      "replaceString": "PYTHON_VERSION: \"3.11\"",
      "updates": [
        {
          "bucket": "non-major",
          "newVersion": "3.13",
          "newValue": "3.13",
          "newMajor": 3,
          "newMinor": 13,
          "newPatch": null,
          "updateType": "minor",
          "branchName": "renovate/python-version-updates"
        }
      ],
      "packageName": "registry.gitlab.developers.cam.ac.uk/uis/devops/infra/dockerimages/python",
      "versioning": "docker",
      "warnings": [],
      "registryUrl": "https://registry.gitlab.developers.cam.ac.uk",
      "lookupName": "uis/devops/infra/dockerimages/python",
      "currentVersion": "3.11",
      "isSingleVersion": true,
      "fixedVersion": "3.11"
    }
  ],
  "matchStrings": ["PYTHON_VERSION: \"(?<currentValue>.*?)\""],
  "depNameTemplate": "registry.gitlab.developers.cam.ac.uk/uis/devops/infra/dockerimages/python",
  "datasourceTemplate": "docker",
  "depTypeTemplate": "python-version-ci",
  "packageFile": ".gitlab/webapp.gitlab-ci.yml"
}