bugfix: avoid endless loops on contract negotiation sending failure

[ndr-brt]

What this PR changes/adds

Avoid endless loops on contract negotiation sending failures.

Why it does that

To avoid log flooding.

Further notes

• used the SendRetryManager component, generalized to work also with negotiations and moved to the state-machine-lib module
• introduced Entity interface, that could be a starting point for Core: base classes for entities and in-memory store #1463 (used an interface because it was the easiest thing to do, probably a class would fit better)
• introduced an internal contract negotiation manager component called AsyncSendResultHandler that takes care of handling the async results, this was to remove a lot of duplication, and actually makes the code more readable.
• I really think the SendRetryManager is pretty trivial to understand, I have in mind a refactor that could make everything more understandable, will propose it in another PR as this brought already enough modifications.

Linked Issue(s)

Closes #1487

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 #1489 (2230ec4) into main (50c941a) will increase coverage by 0.00%.
The diff coverage is 80.95%.

@@           Coverage Diff           @@
##             main    #1489   +/-   ##
=======================================
  Coverage   67.16%   67.17%           
=======================================
  Files         716      716           
  Lines       15972    15989   +17     
  Branches     1057     1046   -11     
=======================================
+ Hits        10728    10740   +12     
- Misses       4770     4774    +4     
- Partials      474      475    +1     

Impacted Files	Coverage Δ
...connector/transfer/core/CoreTransferExtension.java	0.00% <0.00%> (ø)
...sfer/core/transfer/TransferProcessManagerImpl.java	81.54% <ø> (ø)
...main/contract/negotiation/ContractNegotiation.java	0.00% <0.00%> (ø)
...tor/spi/types/domain/transfer/TransferProcess.java	76.47% <ø> (ø)
...iation/ConsumerContractNegotiationManagerImpl.java	86.89% <78.18%> (-0.89%)	⬇️
...iation/ProviderContractNegotiationManagerImpl.java	90.22% <78.57%> (-0.64%)	⬇️
...egotiation/AbstractContractNegotiationManager.java	94.04% <86.11%> (-5.96%)	⬇️
...mon/statemachine/retry/EntitySendRetryManager.java	89.47% <100.00%> (ø)
...ceconnector/contract/ContractServiceExtension.java	95.65% <100.00%> (+0.57%)	⬆️

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