DXCDT-460: Refactor how we check for 404 errors

[sergiught]

🔧 Changes

In this PR we're refactoring how we do the 404 checks and triggering a resource deletion. We're now consistently doing that in the read, update and delete funcs, but the create should continue to raise the error to let the user know something went wrong during creation.

📚 References

🔬 Testing

📝 Checklist

• All new/changed/fixed functionality is covered by tests (or N/A)
• I have added documentation for all new/changed functionality (or N/A)

[codecov-commenter]

Codecov Report

Merging #727 (ec4924c) into v1 (ec4924c) will not change coverage.
The diff coverage is n/a.

❗ Current head ec4924c differs from pull request most recent head c4cf094. Consider uploading reports for the commit c4cf094 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##               v1     #727   +/-   ##
=======================================
  Coverage   87.52%   87.52%           
=======================================
  Files          87       87           
  Lines       13237    13237           
=======================================
  Hits        11586    11586           
  Misses       1248     1248           
  Partials      403      403           

[sergiught]

Codecov is hiding the glorious fact that this takes our coverage to 89.74% https://app.codecov.io/gh/auth0/terraform-provider-auth0/tree/patch%2FDXCDT-460-errors-404