core: dispatch contractdefinition events

[ndr-brt]

What this PR changes/adds

Dispatch ContractDefinition events

Why it does that

To permit asynchronous notifications

Further notes

• Moved observable interfaces & classes to the spi

Linked Issue(s)

Closes #1436

Checklist

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

[codecov-commenter]

Codecov Report

Merging #1538 (db65f0f) into main (385be86) will decrease coverage by 0.05%.
The diff coverage is 56.25%.

@@            Coverage Diff             @@
##             main    #1538      +/-   ##
==========================================
- Coverage   67.16%   67.10%   -0.06%     
==========================================
  Files         736      741       +5     
  Lines       16139    16182      +43     
  Branches     1048     1048              
==========================================
+ Hits        10839    10859      +20     
- Misses       4823     4846      +23     
  Partials      477      477              

Impacted Files	Coverage Δ
...or/api/datamanagement/asset/AssetApiExtension.java	100.00% <ø> (ø)
...datamanagement/asset/service/AssetServiceImpl.java	100.00% <ø> (ø)
...tamanagement/asset/service/EventAssetListener.java	100.00% <ø> (ø)
...anagement/policy/PolicyDefinitionApiExtension.java	100.00% <ø> (ø)
...nt/policy/service/PolicyDefinitionServiceImpl.java	94.11% <ø> (ø)
...definition/observe/ContractDefinitionListener.java	0.00% <0.00%> (ø)
...tion/observe/ContractDefinitionObservableImpl.java	0.00% <0.00%> (ø)
.../contractdefinition/ContractDefinitionCreated.java	0.00% <0.00%> (ø)
.../contractdefinition/ContractDefinitionDeleted.java	0.00% <0.00%> (ø)
...vent/policydefinition/PolicyDefinitionCreated.java	100.00% <ø> (ø)
... and 11 more

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