Migration from sheadawson/silverstripe-linkable

[maxime-rainville]

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

Acceptance criteria

• An automated task exists to converts sheadawson/silverstripe-linkable data to v4 linkfield format.
  • The task accounts for versioning and all pre-existing links are assumed to be published.
  • Task can be extended to accommodate unusual usage of LinkField.
• 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 covers how to completely remove the linkable module.
• Guidance mentions feature gap between two linkfield implementations, but leave the developer to resolve these issue themselves.
• Migration task is marked as @deprecated.
• The task is disabled by default.

PR

• https://github.com/silverstripe/silverstripe-linkfield/pull/261

[GuySartorelli]

FYI @sabina-talipova We discussed in standup today - these migration tasks have missed the cut-off for making it into the 4.0.0 stable release, so we'll need to target the 4 branch for them to be included in a future minor release.

[sabina-talipova]

For further implementation, it is required that this PR be merged into the main branch 4 first. New trait is required.

[GuySartorelli]

@sabina-talipova the gorriecoe migration PRs have all been merged now

[GuySartorelli]

PR merged