Move imports into relevant functions and branches

[CasperWA]

The imports of aiida_optimade and requests have been moved into the relevant functions and branches.

aiida_optimade is used to retrieve the __version__ if --patch is used when updating the version.
Only if --patch is passed will aiida_optimade be imported.

requests is only used when updating the optimade package version.

[codecov]

Codecov Report

Merging #154 into develop will increase coverage by 0.44%.
The diff coverage is 92.64%.

@@             Coverage Diff             @@
##           develop     #154      +/-   ##
===========================================
+ Coverage    90.15%   90.59%   +0.44%     
===========================================
  Files           28       28              
  Lines         1056     1095      +39     
===========================================
+ Hits           952      992      +40     
+ Misses         104      103       -1     

Flag	Coverage Δ
pytest	90.59% <92.64%> (+0.44%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiida_optimade/cli/cmd_calc.py	84.48% <88.00%> (+5.75%)	⬆️
aiida_optimade/entry_collections.py	92.67% <90.90%> (-0.23%)	⬇️
aiida_optimade/cli/cmd_init.py	95.74% <96.00%> (+4.56%)	⬆️
aiida_optimade/common/logger.py	100.00% <100.00%> (ø)

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