Review 5.2 changelog

[maxime-rainville]

As a developer contemplating a 5.2 upgrade, I want clear and concise information about what has changed so I can plan my upgrade with ease.

Acceptance criteria

1. List of commits is reviewed to identify noteworthy changes not currently appearing in the main body of changelog.
2. Full changelog is reviewed for readability and to make sure no key details are missing.
3. Changelog follows our Web Writing Style Guide (only available to Silverstripe staff).
4. Since the linkfield migrations didn't make it, changelog gives some indication about what to do if updating from an old version of linkfield.

Exclude

• Warning about the change of support level for 4.

PRs

• Review of the Silverstripe CMS 5.2.0 changelog #482

[sabina-talipova]

PR has been merged. Task is completed.