docs(changelog): fix headers consistency

[vtsvetkov-splunk]

Issue number:

PR Type

What kind of change does this PR introduce?

• [ ] Feature
• [ ] Bug Fix
• [ ] Refactoring (no functional or API changes)
• [x] Documentation Update
• [ ] Maintenance (dependency updates, CI, etc.)

Changes

• Fix all headers to have proper table of content, added level 1 heading
• Set up pipelines to keep the level 1 heading, while appending releases at the top. Source - https://github.com/semantic-release/changelog/blob/master/test/prepare.test.js#L72

Before

After

User experience

Convenient navigation

Checklist

If an item doesn't apply to your changes, leave it unchecked.

• [x] I have performed a self-review of this change according to the development guidelines
• [ ] Tests have been added/modified to cover the changes (testing doc)
• [ ] Changes are documented
• [x] PR title and description follows the contributing principles