SUPPORT-28804 add custom deserializer for attrs in import api

[lojzatran]

Can't deserialize to nested type because the Java type is not available: https://github.com/commercetools/commercetools-sdk-java-v2/blob/main/commercetools/commercetools-sdk-java-importapi/src/main/java-generated/com/commercetools/importapi/models/productvariants/Attribute.java

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 87.12446% with 30 lines in your changes missing coverage. Please review.

Project coverage is 10.06%. Comparing base (a248061) to head (9167a78). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
.../commercetools/api/json/AttributeDeserializer.java	84.61%	11 Missing and 7 partials :warning:
...ols/importapi/json/ErrorAttributeDeserializer.java	91.96%	5 Missing and 4 partials :warning:
.../commercetools/api/json/AtrributeDeserializer.java	0.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #748 +/- ## =========================================== + Coverage 9.89% 10.06% +0.16% - Complexity 1899 1944 +45 =========================================== Files 6816 6818 +2 Lines 66502 66621 +119 Branches 268 279 +11 =========================================== + Hits 6580 6704 +124 + Misses 59754 59743 -11 - Partials 168 174 +6 ```

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[barbara79]

LGTM 👍