[JENKINS-68755] Add support for explicit user and group assignment

[mawinter69]

Adding support to explicitly assign a role to a user or a group. This avoids confusion when a name matches both. A warning will be shown on the role assignment page for ambiguous entries with the possibility to make this a user or a group assignment.

❗ This is an incompatible change and after migration, going back to the previous version will require to undo the config changes. While the changes to the config.xml can be read by older versions, you can run into problems with duplicate entries.
Changes done on Configuration As Code yaml files need to be reverted to the old format before downgrading.

Config file changes

The new version can read an existing config.xml file. After startup of Jenkins with the new plugin version, the config.xml will be automatically saved with the new format. The new format basically just adds a new attribute to the sids

  <assignedSIDs>
    <sid>adminuser</sid>
    <sid>admingroup</sid>
  </assignedSIDs>

becomes (after applying user/group assignment via the UI)

  <assignedSIDs>
    <sid type="USER">adminuser</sid>
    <sid type="GROUP">admingroup</sid>
  </assignedSIDs>

(Without applying user/group it becomes

    <sid type="EITHER">adminuser</sid>

)

Configuration as Code changes

To read Configuration as code yaml files in the old format, please add the following to your casc yaml.

configuration-as-code:
  version: 1
  deprecated: warn

Without this addition startup will fail.

After starting Jenkins go to Assign Roles page and select for each entry in the table if the entry should be a user or a group.
Once all entries are adjusted save the changes. You can then go to Configuration as Code and look at the new format.
If you want to manually change you yaml files replace all occurrences of

assignments:
  - usersid1
  - usersid2
  - groupsid1
  - groupsid2

with

entries:
  - user: usersid1
  - user: usersid2
  - group: groupsid1
  - group: groupsid2

API Changes

The plugin APIs have significantly changed. Plugins that depend on role-strategy will probably need to be adjusted as well or might not work as expected (ownership-plugin, dynamic_extended_choice_parameter). Existing groovy scripts should be adjusted accordingly to avoid creating ambiguous entries.

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[basil]

Required Configuration as Code plugin tests to be adapted: jenkinsci/configuration-as-code-plugin#2357