Document current approach to creating API endpoints in the CMS

[maxime-rainville]

Acceptance criteria

• Common approach to creating CMS endpoints in the CMS are identified and documented.
• Common pitfall (e.g. permissions check, error handling) are called out.

Related

• Standardise how we create API/FormSchema endpoint in the CMS silverstripe-admin#1589

Follow up card

• Document explains how to create Form Schema (Maybe spin up as a separate card and go into the JS part as well.)

Notes

• private static string $required_permission_codes = 'CMS_ACCESS_CMSMain'; is required on LinkFieldController so that non-admins can access endpoints, so possibly this is general a requirement for all controllers that extend LeftAndMain

PRs

• DOC CMS JSON API's #445
• NEW Add jsonSuccess() silverstripe-admin#1658
• ENH Standardise API responses silverstripe-linkfield#184

[GuySartorelli]

Assigning back to Steve to do whatever needs done with the linkfield PR (haven't looked at it yet)

[GuySartorelli]

PRs merged