expose create_dummy() to public API.

[lballerio]

In this PR we are exposing in the public API create_dummy function;
this choice was made for Qibocal #1624.

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.95%. Comparing base (f8be2ad) to head (c743fa8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1535   +/-   ##
=======================================
  Coverage   38.94%   38.95%           
=======================================
  Files         120      120           
  Lines        6222     6223    +1     
=======================================
+ Hits         2423     2424    +1     
  Misses       3799     3799           

Flag	Coverage Δ
unittests	38.95% <100.00%> (+<0.01%)	⬆️

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

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[alecandido]

While not 100% sure about its usage in qiboteam/qibocal#1624, create_dummy() was certainly intended for public usage.

The idea was to be able to run something ultra-fast with meaningless but correctly-shaped results, to simplify some testing.
For the meaningful counterpart we have the emulator, but dummy still has a role for quick prototyping, Where having some meaningless results at hand is still better than not being able to run at all.

We may change its interface in the future. But, since this is meant for general usage, it will be rightfully considered a breaking change