docs: add core changelog

[julienrbrt]

Description

I had to do it manually (git log --pretty=oneline core/v0.6.1..core/v0.7.0 ./core/** for each tag and then cherry-picking the PR) because the changelog generation brings too much false positive.

I think for getting a better changelog generation and remove the replace hell we have in our mono-repo, we should greatly limit the number of PRs touching multiples go mod and make them more contained.
It seems like we attempted doing this a while ago (see description), but I wonder why it hasn't sticked #13115. The downside doing that is that we need to tag way more.
I do not think we can get both of best world (pretty generated changelogs and big PRs). Personally I am fine with manual changelogs, but we really need to keep them up to date. Doing them manually from scratch isn't funny 😅

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Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)