Deprecate initial capacity

[alonre24]

Describe the changes in the pull request

Deprecate this parameter, always initialize an index with 0 capacity. The goal here is to have the resize (which relies on the index capacity) aligned for the vector blocks and other data structures. As a consequence, in a tiered index, we can make sure that we resize blocks only when we are locked exclusively.

Mark if applicable

• [ ] This PR introduces API changes
• [ ] This PR introduces serialization changes

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.93%. Comparing base (5011de8) to head (3514bb2). Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #546      +/-   ##
==========================================
- Coverage   97.02%   96.93%   -0.09%     
==========================================
  Files         100      100              
  Lines        5307     5287      -20     
==========================================
- Hits         5149     5125      -24     
- Misses        158      162       +4     

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