update wx_shape validator optional syntax

[CagtayFabry]

Changes

see #184

Related Issues

Closes #184

Checks

• updated CHANGELOG.rst
• updated tests
• updated doc/
• update example/tutorial notebooks
• update manifest file

[codecov]

Codecov Report

Merging #571 (0fce9ba) into master (02ff5a4) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 0fce9ba differs from pull request most recent head b2c167e. Consider uploading reports for the commit b2c167e to get more accurate results

@@            Coverage Diff             @@
##           master     #571      +/-   ##
==========================================
- Coverage   94.87%   94.86%   -0.02%     
==========================================
  Files          93       93              
  Lines        5734     5742       +8     
==========================================
+ Hits         5440     5447       +7     
- Misses        294      295       +1     

Impacted Files	Coverage Δ
weldx/asdf/util.py	86.52% <100.00%> (+0.07%)	⬆️
weldx/asdf/validators.py	98.73% <100.00%> (-0.61%)	⬇️

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[CagtayFabry]

I have added another way to indicate a optional shape requirement by enclosing the list in braces for instances where wx_shape is defined directly at the property

wx_shape: ([1,2,a])