refactor(SPV-1020): move paymail servant to separate package and use it in engine

[dorzepowski]

Context

• in the next step of new create draft transaction method we need to integrate with paymail
• using paymail servant when it was in engine from the other package used by engine is ending with circular deps error
• I changed the name of PaymailServant to paymail.ServiceClient - to not have redundant Paymail in package and struct name
• most important functionality: getCapabilities with cacheing, was done by private function in engine, while it seems like a very useful method that could be used by any thing, that's why I moved it to the paymail.ServiceClient
• I moved some of the functions from paymail.go to be a methods on paymail service client and make the current code that was using them to use them with help of paymail.ServiceClient
• I moved a paymail_test.go but it has several things that was mocking paymail host server
• I created a method to setup paymail client with connection to mocked paymail host server and with methods to help to setup this paymail host server.

Pull Request Checklist

• 📖 I created my PR using provided : CODE_STANDARDS
• 📖 I have read the short Code of Conduct: CODE_OF_CONDUCT
• 🏠 I tested my changes locally.
• ✅ I have provided tests for my changes.
• 📝 I have used conventional commits.
• 📗 I have updated any related documentation.
• 💾 PR was issued based on the Github or Jira issue.

[github-actions]

Manual Tests

💚 Manual testing by @chris-4chain resulted in success.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 64.57143% with 124 lines in your changes missing coverage. Please review.

Project coverage is 46.42%. Comparing base (ba50ac3) to head (1332f5e).

Files with missing lines	Patch %	Lines
engine/paymail/paymail_service_client.go	57.60%	34 Missing and 5 partials ⚠️
engine/tester/paymailmock/mock_paymail_client.go	65.45%	36 Missing and 2 partials ⚠️
engine/tester/paymailmock/mock_capability.go	59.25%	8 Missing and 3 partials ⚠️
engine/paymail/paymail_payload_format.go	0.00%	8 Missing ⚠️
engine/client_internal.go	41.66%	5 Missing and 2 partials ⚠️
...ne/tester/paymailmock/mock_capability_factories.go	83.33%	6 Missing ⚠️
engine/tester/cache.go	0.00%	5 Missing ⚠️
engine/model_draft_transactions.go	25.00%	0 Missing and 3 partials ⚠️
engine/tester/logger.go	0.00%	2 Missing ⚠️
...ine/tester/paymailmock/mock_paymail_domain_name.go	87.50%	2 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #697      +/-   ##
==========================================
+ Coverage   46.32%   46.42%   +0.09%     
==========================================
  Files         290      296       +6     
  Lines       12833    13024     +191     
==========================================
+ Hits         5945     6046     +101     
- Misses       6296     6386      +90     
  Partials      592      592              

Flag	Coverage Δ
unittests	46.42% <64.57%> (+0.09%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
engine/action_contact.go	40.65% <100.00%> (-0.95%)	⬇️
engine/paymail.go	0.00% <ø> (-44.83%)	⬇️
...gine/tester/paymailmock/paymail_service_fixture.go	100.00% <100.00%> (ø)
engine/client.go	65.15% <0.00%> (ø)
engine/client_paymail.go	86.36% <83.33%> (-1.14%)	⬇️
engine/model_transaction_config.go	81.76% <88.88%> (+0.62%)	⬆️
engine/tester/logger.go	0.00% <0.00%> (ø)
...ine/tester/paymailmock/mock_paymail_domain_name.go	87.50% <87.50%> (ø)
engine/model_draft_transactions.go	74.80% <25.00%> (-0.68%)	⬇️
engine/tester/cache.go	62.50% <0.00%> (-11.58%)	⬇️
... and 6 more

... and 1 file with indirect coverage changes

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[wregulski]

Please assign to PR :D