feat: add headerStart to steps to allow building a timeline

[amanabiy]

Description

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.57%. Comparing base (45502c0) to head (12ac93e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4687   +/-   ##
=======================================
  Coverage   97.57%   97.57%           
=======================================
  Files         948      948           
  Lines       30507    30516    +9     
  Branches    11164    11169    +5     
=======================================
+ Hits        29767    29776    +9     
- Misses        693      733   +40     
+ Partials       47        7   -40     

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