Support persisting empty fields in StructToData

[mgyucht]

Changes

Some APIs legitimately return empty objects in fields, but StructToData does not persist these objects (e.g. #3351). This is caused by a filter in collectionToMaps that removes data structures that don't have any non-optional fields or optional fields set to a non-empty/non-nil value.

This PR removes this check. I need to do a bit more work to verify the impact of removing this on the rest of the provider.

Tests

• make test run locally
• relevant change in docs/ folder
• covered with integration tests in internal/acceptance
• relevant acceptance tests are passing
• using Go SDK

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.44%. Comparing base (d29070e) to head (6617754).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3362      +/-   ##
==========================================
+ Coverage   83.43%   83.44%   +0.01%     
==========================================
  Files         176      176              
  Lines       16219    16221       +2     
==========================================
+ Hits        13532    13536       +4     
+ Misses       1865     1864       -1     
+ Partials      822      821       -1     

Files	Coverage Δ
common/reflect_resource.go	84.09% <ø> (+0.32%)	⬆️

... and 1 file with indirect coverage changes

[alexott]

thank you!

[hectorcast-db]

We should be careful of APIs which "default" to empty structs / do not differentiate between not-set and empty struct.
If a user does not set the value, and the API returns an empty struct, there will be always a diff.

[alexott]

@hectorcast-db can we merge it, or we need to work on it further?

[hectorcast-db]

@alexott @mgyucht
We discussed offline. It looks good to me, but I think that @mgyucht still wanted to run some tests.

[mgyucht]

I was concerned that this might exacerbate some issues with suppress diff, as it is will add empty dictionaries into state which might need diff suppression. However, I realized that that would only be needed if the API returned non-nil/empty values, which would always end up in the state anyways. So I think that isn't a concern, so we can merge this.