Allow to opt-out index tracker reset on locale update

Note: the issue doesn't happen when manually updating interface or config translations

@maintainers: Hi! I'm willing to provide a fix but I'd need a bit of guidance because I can't figure out where this is happening. Would you help me, please?

Thanks for reporting this issue and sorry for the delay!
However, I’m afraid I cannot reproduce this problem:

$ drush sapi-s
 --------------------- ----------------------- ------------ --------- ------- 
  ID                    Name                    % Complete   Indexed   Total  
 --------------------- ----------------------- ------------ --------- ------- 
  default_index         Default content index   100%         233       233    
 --------------------- ----------------------- ------------ --------- -------
$ drush locale:update
…
$ drush sapi-s
 --------------------- ----------------------- ------------ --------- ------- 
  ID                    Name                    % Complete   Indexed   Total  
 --------------------- ----------------------- ------------ --------- ------- 
  default_index         Default content index   100%         233       233    
 --------------------- ----------------------- ------------ --------- -------

Am I doing something wrong for reproducing? Otherwise it seems some custom code or third-party module is to blame for this issue. You’d have to track calls to the appropriate method(s) on \Drupal\search_api\Entity\Index (probably reindex(), clear() or rebuildTracker()) or the tracker plugin and log the backtrace to figure out where the call is coming from.