feat(container): add destroy_registry field to container namespace

[Codelax]

Fix #1215
Add a new field to scaleway_container_namespace

resource scaleway_container_namespace main {
    name = "test-cr-ns-01"
    destroy_registry = true
}

It defaults to false and can be set to true to delete registry namespace after container namespace

[codecov-commenter]

Codecov Report

Merging #1321 (5092fa9) into master (d4210a1) will decrease coverage by 0.02%.
The diff coverage is 62.96%.

@@            Coverage Diff             @@
##           master    #1321      +/-   ##
==========================================
- Coverage   70.15%   70.13%   -0.03%     
==========================================
  Files         102      102              
  Lines       16422    16445      +23     
==========================================
+ Hits        11521    11533      +12     
- Misses       3922     3929       +7     
- Partials      979      983       +4     

Impacted Files	Coverage Δ
scaleway/resource_container_namespace.go	70.68% <62.96%> (-2.83%)	⬇️

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