Implement create_empty and create_empty_like convenience methods for Dataset creation.

[dmitriyrepin]

#687
Redone without any code reuse.

[codecov]

Codecov Report

❌ Patch coverage is 91.78082% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.67%. Comparing base (c3ba558) to head (c89f7e2).
⚠️ Report is 247 commits behind head on main.

Files with missing lines	Patch %	Lines
src/mdio/api/create.py	73.43%	6 Missing and 11 partials ⚠️
tests/integration/test_z_create_empty.py	97.26%	1 Missing and 4 partials ⚠️
tests/integration/testing_helpers.py	95.55%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #736 +/- ##
==========================================
+ Coverage 85.30% 87.67% +2.36% 
==========================================
Files 46 89 +43 Lines 2219 5096 +2877 Branches 306 345 +39 ==========================================
+ Hits 1893 4468 +2575 - Misses 281 541 +260 - Partials 45 87 +42 

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