fix: move password migration hook config

[hperl]

This moves the password migration hook to

selfservice:
  methods:
    password:
      config:
        migrate_hook:
          ...

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.23%. Comparing base (a84fb3f) to head (49a5788).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3986   +/-   ##
=======================================
  Coverage   78.23%   78.23%           
=======================================
  Files         365      365           
  Lines       25586    25586           
=======================================
+ Hits        20016    20018    +2     
+ Misses       4040     4039    -1     
+ Partials     1530     1529    -1     

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