FLUT-996020 - [Others] Added user guidelines for custom plotband feature.#1379

sfHariHaraSudhan merged 2 commits intodevelopmentsyncfusion-content/flutter-docs:developmentfrom

FLUT-996020-Plotband-ugsyncfusion-content/flutter-docs:FLUT-996020-Plotband-ugCopy head branch name to clipboard