Add centerAltitude to style spec

[NathanMOlson]

Launch Checklist

Add centerAltitude to style spec, as discussed here: #851

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• Briefly describe the changes in this PR.
• Link to related issues.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Add an entry to CHANGELOG.md under the ## main section.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.73%. Comparing base (30d9ad4) to head (835d69a).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #875   +/-   ##
=======================================
  Coverage   92.73%   92.73%           
=======================================
  Files         105      105           
  Lines        4681     4683    +2     
  Branches     1322     1323    +1     
=======================================
+ Hits         4341     4343    +2     
  Misses        340      340           

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[HarelM]

LGTM.
@ibesora @louwers please approve as well.