Docs: Heatmap (#531)

* feat(heatmap): docs and images

* Update components/chart/types/heatmap.md

Co-authored-by: Dimo Dimov <961014+dimodi@users.noreply.github.com>

* chore(heatmap): fix copy-paste error

* chore(heatmap): add ctor for the model class

* chore(heatmap) multiple fixes

* chore(heatmap): delete unclear sentence

* Update components/chart/types/heatmap.md

Co-authored-by: Dimo Dimov <961014+dimodi@users.noreply.github.com>

Co-authored-by: Dimo Dimov <961014+dimodi@users.noreply.github.com>

Author: svdimitr