feat(instance_server): prevent usage of routed_ip_enabled as false

[Codelax]

NAT IPs are coming to an end, users received emails to ask them to migrate. If not done manually, migration will be forced.
I'm changing the provider so it blocks users from using NAT IPs. Goal is to make them consider manually migrating before being forced.

If you previously used NAT IPs, you can remove the explicit field configuration (remove: routed_ip_enabled: false). If not set, the provider will be able to work after the migration. Otherwise the provider will block after migration as it will not be able to migrate back from nat to routed.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 10.00000% with 18 lines in your changes missing coverage. Please review.

Project coverage is 71.12%. Comparing base (fe86049) to head (d15f02b).
Report is 199 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/services/instance/server.go	0.00%	11 Missing ⚠️
internal/services/instance/ip.go	22.22%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2763      +/-   ##
==========================================
- Coverage   71.43%   71.12%   -0.32%     
==========================================
  Files         277      328      +51     
  Lines       35875    32916    -2959     
==========================================
- Hits        25628    23411    -2217     
+ Misses       8028     7254     -774     
- Partials     2219     2251      +32     

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