Rename vendor error code and update documentation#316

tiyash-basu-frequenz merged 2 commits intofrequenz-floss:v0.x.xfrequenz-floss/frequenz-api-common:v0.x.xfrom

tiyash-basu-frequenz:rename_vendor_error_codetiyash-basu-frequenz/frequenz-api-common:rename_vendor_error_codeCopy head branch name to clipboard