DXCDT-347: Allow updating templates for phone-message-hook in auth0 guardian

[sergiught]

🔧 Changes

As noted in #433, we erroneously do not allow updating the templates when a custom provider is selected for the guardian resource. This PR aims at fixing that.

📚 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

Base: 87.11% // Head: 87.12% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (34091f7) compared to base (ac1ab8e).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #444   +/-   ##
=======================================
  Coverage   87.11%   87.12%           
=======================================
  Files          42       42           
  Lines        9192     9193    +1     
=======================================
+ Hits         8008     8009    +1     
  Misses        910      910           
  Partials      274      274           

Impacted Files	Coverage Δ
internal/provider/resource_auth0_guardian.go	93.73% <100.00%> (+0.04%)	⬆️
internal/provider/structure_auth0_guardian.go	73.82% <100.00%> (-0.13%)	⬇️

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