feat(instance): improve support of windows based servers

[Codelax]

• Add --wait to scw instance server get-rdp-password.
• Add admin-password-encryption-ssh-key-id with completion to scw instance server {create,update}
• Make admin-password-encryption-ssh-key-id required when creating a Windows server. This avoid confusion as password will not be generated without a ssh key id.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 74.50980% with 13 lines in your changes missing coverage. Please review.

Project coverage is 72.50%. Comparing base (5bf53e0) to head (4a44ed1).
Report is 90 commits behind head on master.

Files	Patch %	Lines
...ternal/namespaces/instance/v1/custom_server_rdp.go	59.37%	11 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3863      +/-   ##
==========================================
- Coverage   75.45%   72.50%   -2.95%     
==========================================
  Files         202      287      +85     
  Lines       44323    51022    +6699     
==========================================
+ Hits        33444    36995    +3551     
- Misses       9653    12512    +2859     
- Partials     1226     1515     +289     

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