models/team: Replace String with &str for NewTeam struct fields

[Turbo87]

For INSERT queries there is no need for allocations, so let's replace them with regular references.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.71%. Comparing base (eccda03) to head (4804e6b).
Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9686   +/-   ##
=======================================
  Coverage   88.71%   88.71%           
=======================================
  Files         287      287           
  Lines       29339    29338    -1     
=======================================
  Hits        26028    26028           
+ Misses       3311     3310    -1     

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