987470-Add UG for ExcelKnownColors in XlsIO#1578

KarthikaSF4773 wants to merge 3 commits intohotfix/hotfix-v31.2.2syncfusion-content/document-processing-docs:hotfix/hotfix-v31.2.2from

987470-ExcelKnownColorssyncfusion-content/document-processing-docs:987470-ExcelKnownColorsCopy head branch name to clipboard