feat(SPV-1300): experimental new tx flow feature flag

[chris-4chain]

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 @wregulski resulted in success.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 53.96825% with 29 lines in your changes missing coverage. Please review.

Project coverage is 45.92%. Comparing base (1acad0e) to head (adb4b66).

Files with missing lines	Patch %	Lines
engine/paymail/paymail_service_provider.go	0.00%	17 Missing ⚠️
engine/client_options.go	20.00%	4 Missing ⚠️
config/config_to_options.go	0.00%	3 Missing ⚠️
engine/client_internal.go	81.25%	1 Missing and 2 partials ⚠️
engine/client.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #829      +/-   ##
==========================================
- Coverage   45.96%   45.92%   -0.05%     
==========================================
  Files         369      371       +2     
  Lines       17820    17856      +36     
==========================================
+ Hits         8191     8200       +9     
- Misses       9022     9047      +25     
- Partials      607      609       +2     

Flag	Coverage Δ
unittests	45.92% <53.96%> (-0.05%)	⬇️

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

Files with missing lines	Coverage Δ
actions/register.go	100.00% <100.00%> (ø)
actions/transactions/routes.go	100.00% <100.00%> (ø)
config/config.go	33.33% <ø> (ø)
engine/testabilities/fixture_configopts.go	100.00% <100.00%> (ø)
engine/testabilities/fixture_engine.go	90.26% <ø> (ø)
server/handlers/manager.go	100.00% <100.00%> (ø)
server/server.go	8.33% <100.00%> (ø)
engine/client.go	53.62% <0.00%> (-0.34%)	⬇️
config/config_to_options.go	0.00% <0.00%> (ø)
engine/client_internal.go	58.04% <81.25%> (-0.25%)	⬇️
... and 2 more

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[wregulski]

Great job! 👌