Backport of Changelog process improvements into v1.11

[github-actions]

Backport

This PR is auto-generated from #36334 to be assessed for backporting due to the inclusion of the label 1.11-backport.

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Warning automatic cherry-pick of commits failed. If the first commit failed,
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The person who merged in the original PR is:
@DanielMSchmidt
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.

merge conflict error: POST https://api.github.com/repos/hashicorp/terraform/merges: 409 Merge conflict []

The below text is copied from the body of the original PR.

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This PR solves two problems in the changelog process

1. We only want to include experiments if we are doing an alpha release and in the dev changelog
2. When a branch is set up for the new minor version when doing a beta we want to make sure any changes coming in to that branch via the backport process are only included in the old minor release and not the next one as well. To solve this we now have unreleased folder for changes that are not yet released in the next minor and backported folder for changes that will be backported.

Fixes #

Target Release

1.11.x

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.

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Overview of commits

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