Shorten the changelog in the readme file

[stefan-cotitosu]

What problem does this address?

As part of the plugin localization initiative, we need to optimize the readme.txt file.

What is your proposed solution?

In the readme.txt file, remove changelogs from all previous versions. Retain only the most recent changelog and provide a link to GitHub for changelogs of previous versions. Here is an example of how was this implemented before.

Current behavior vs Expected behavior

Will this feature require documentation? (Optional)

No.