Add configuration setting force_new

[forman]

Added configuration setting force_new, which forces creation of a new target dataset. An existing target dataset (and its lock) will be permanently deleted before appending of slice datasets begins.

Closes #72

Checklist (strike out non-applicable):

• Changes documented in CHANGES.md
• Related issue exists and is referred to in the PR description and CHANGES.md
• Added docstrings and API docs for any new/modified user-facing classes and functions
• Changes/features documented in docs/*
• Unit-tests adapted/added for changes/features
• Test coverage remains or increases (target 100%)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.92%. Comparing base (2b56f1f) to head (9741c43).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #73      +/-   ##
==========================================
+ Coverage   99.85%   99.92%   +0.07%     
==========================================
  Files          26       26              
  Lines        1372     1396      +24     
==========================================
+ Hits         1370     1395      +25     
+ Misses          2        1       -1     

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[thomasstorm]

Some minor suggestions, include or drop as you wish. Looks like a good feature!