support string units in get_groove

[CagtayFabry]

Changes

enable string syntax for unit in get_groove and update tutorial

Checks

• updated CHANGELOG.md
• update example/tutorial notebooks

[review-notebook-app]

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[codecov]

Codecov Report

Merging #416 (cc254bd) into master (047d699) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #416   +/-   ##
=======================================
  Coverage   97.27%   97.27%           
=======================================
  Files          87       87           
  Lines        5352     5352           
=======================================
  Hits         5206     5206           
  Misses        146      146           

Impacted Files	Coverage Δ
weldx/welding/groove/iso_9692_1.py	99.51% <100.00%> (ø)

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