feat: split Dtos in InputDto and OutputDto for Asset and ContractDefinition

[ndr-brt]

What this PR changes/adds

Split

• AssetDto in AssetInputDto and AssetOutputDto
• ContractDefinitionDto in ContractDefinitionInputDto and ContractDefinitionOutputDto

Why it does that

To improve APIs, as currently the spec are stating that a createdAt field can be passed from the client, but that's not true as that field is valued by the EDC itself

Further notes

• remove duplication between TransformerContextImpl and DtoTransformerContext that were the pretty much the same class.
• improve validation on the ids, as they shouldn't be mandatory from the client but they should be created by the EDC as random UUID by default (as done for PolicyDefinition, ContractNegotiation, TransferProcess and DataRequest)
• make the asset and contract definition transformers "NPE proof". This would lead to a subsequent refactor in another PR as all the transformer should handle the "null input" correctly

Linked Issue(s)

Closes #1796

Checklist

• added appropriate tests?
• performed checkstyle check locally?
• added/updated copyright headers?
• documented public classes/methods?
• added/updated relevant documentation?
• assigned appropriate label? (exclude from changelog with label no-changelog)
• formatted title correctly? (take a look at the CONTRIBUTING and styleguide for details)

[paullatzelsperger]

I have not yet looked at this in greater detail, but my inner monk somehow would immediately feel more comfortable if they were named RequestDto and ResponseDto

[ndr-brt]

I have not yet looked at this in greater detail, but my inner monk somehow would immediately feel more comfortable if they were named RequestDto and ResponseDto

@paullatzelsperger makes total sense to me. Done

[codecov-commenter]

Codecov Report

Merging #1797 (2f523f5) into main (fca34e5) will decrease coverage by 57.14%.
The diff coverage is 0.00%.

@@              Coverage Diff              @@
##               main    #1797       +/-   ##
=============================================
- Coverage     67.78%   10.63%   -57.15%     
- Complexity        0      485      +485     
=============================================
  Files           800      802        +2     
  Lines         16977    17022       +45     
  Branches       1080     1080               
=============================================
- Hits          11508     1811     -9697     
- Misses         4999    15126    +10127     
+ Partials        470       85      -385     

Impacted Files	Coverage Δ
...ids/core/transform/IdsTransformerRegistryImpl.java	0.00% <0.00%> (-65.22%)	⬇️
.../dataspaceconnector/api/model/BaseResponseDto.java	0.00% <0.00%> (ø)
...lipse/dataspaceconnector/api/model/MutableDto.java	0.00% <0.00%> (ø)
...or/api/transformer/DtoTransformerRegistryImpl.java	0.00% <0.00%> (-88.00%)	⬇️
...r/api/datamanagement/asset/AssetApiController.java	0.00% <0.00%> (-97.73%)	⬇️
...or/api/datamanagement/asset/AssetApiExtension.java	0.00% <0.00%> (-100.00%)	⬇️
.../api/datamanagement/asset/model/AssetEntryDto.java	0.00% <ø> (-100.00%)	⬇️
...pi/datamanagement/asset/model/AssetRequestDto.java	0.00% <0.00%> (ø)
...i/datamanagement/asset/model/AssetResponseDto.java	0.00% <0.00%> (ø)
...t/transform/AssetRequestDtoToAssetTransformer.java	0.00% <0.00%> (ø)
... and 550 more

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