Request: Extend API Changelog to list all changes since v4.20

[poikilotherm]

Overview of the Feature Request

With the API changelog introduced in #10060 we now have a place to list important changes to the API.
We should go through the release notes since and including v4.20 to list important events like APIs added, deprecated, broken, fixed, etc.

What kind of user is the feature intended for?
API User

What inspired the request?
#10060 as well as users asking for such an overview.

What existing behavior do you want changed?
None

Any brand new behavior do you want to add to Dataverse?
Nope

Any open or closed issues related to this feature request?

• section in API Guide for changes in behavior and backward incompatibilities  #10060
• v5.6 changes break pydataverse and datalad-dataverse #9549
• Recent changes break the Dataset Migration API #9544
• Breaking API changes in 4.12: RSpace (and other?) integrations broken #5724

[pdurbin]

@poikilotherm thanks for creating this issue and for the related-discussion at https://dataverse.zulipchat.com/#narrow/stream/377090-python/topic/API.20compatibility/near/425911070