Migration from gorriecoe

[maxime-rainville]

As a developer maintaining a project using gorriecoe/silverstripe-linkfield, I have a a clear path and clear guidance on how to migrate to v4.

Acceptance criteria

• An automated task exists to converts gorriecoe/silverstripe-linkfield data to v4 linkfield format.
  • The task accounts for versioning and all pre-existing links are assumed to be published.
  • Task accounts for List of links
  • Task can be extended to accommodate unusual usage of LinkField.
  • Task does not account for custom link types, but provides extensions.
• Clear guidance on how to migrate to LinkField v4 is provided
• Guidance covers the scenario where a project is upgraded all the way from CMS 4.
• Guidance explicitly mentions that it is the developers responsibility to implement logic to cover custom link types.
• Guidance mentions that we are assuming no versioning of gorriecoe links.
• Guidance covers how to completely remove the gorriecoe module.
• Guidance mentions feature gap between two linkfield implementations, but leave the developer to resolve these issue themselves. (e.g. gorriecoe's phone link as conversion methods to different phone number format)
• Migration task is marked as @deprecated.
• The task is disabled by default.

PRs

installer CI showing linkfield passing with the framework PR

• ENH Let unit tests manipulate the DB before loading fixtures silverstripe-framework#11182
• DOC Document creating fixtures in custom DB tables developer-docs#484
• NEW Add migration task from gorriecoe/silverstripe-link #253