feat(igxPivotGrid): Allow setting width:auto so that row dimension is…

[MayaKirova]

… sized based on the rendered cell's width.

Closes #14093

Additional information (check all that apply):

• [ ] Bug fix
• [x] New functionality
• [ ] Documentation
• [ ] Demos
• [ ] CI/CD

Checklist:

• [x] All relevant tags have been applied to this PR
• [x] This PR includes unit tests covering all the new code (test guidelines)
• [ ] This PR includes API docs for newly added methods/properties (api docs guidelines)
• [ ] This PR includes feature/README.MD updates for the feature docs
• [ ] This PR includes general feature table updates in the root README.MD
• [ ] This PR includes CHANGELOG.MD updates for newly added functionality
• [ ] This PR contains breaking changes
• [ ] This PR includes ng update migrations for the breaking changes (migrations guidelines)
• [ ] This PR includes behavioral changes and the feature specification has been updated with them

[tishko0]

I suppose the flickering part is the late rendering of the grid. Now with the fix the headers load and do not flicker, but since the data is async it is noticeable how it gets loaded later and moved to the right side of the cell, so at least in my opinion now only half of the grid flickers. Not sure how to smoothen this feeling, just sharing my 20 cents.