Create visual groupings on release notes page

[akeller]

We need a visual indicator on the release notes UI to help break up the amount of content on the page, but also establish groups.

Some considerations:

• 1:1 mapping is easy - single component feature
• What about a feature that spans core components? Do we group them under "core" or each component?
• Do we need to allow filtering? (Might be v2)
• Do we use collapsible sections (<details>)?

Grouping: I used the buttons to indicate which components are affected by an enhancement. Maybe another tool than "buttons" are more effective to do that (the current buttons impact the heading anchor, which doesn't make sense). I think some sort of grouping is important given we have more an more features for a release. via @MaxTru in https://github.com/camunda/camunda-docs/pull/3800