refactor: move init.py to apis subpackage

[jerome-quere]

As of today because of the scaleway/__init__.py we cannot share the scaleway namespace with other libraries.

Based on https://packaging.python.org/guides/packaging-namespace-packages/ we implement the "pkgutil-style namespace packages" method

[codecov-io]

Codecov Report

Merging #25 into develop will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           develop    #25   +/-   ##
======================================
  Coverage      100%   100%           
======================================
  Files            4      4           
  Lines          101    101           
  Branches        21     21           
======================================
  Hits           101    101

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