docs: Cherry-pick PR #15719: Add v6.8.0 and v6.6.1 changelog entries to dev#15801

summzhan merged 3 commits intodevOfficeDev/microsoft-365-agents-toolkit:devfrom

copilot/cherry-pick-pr-15719-to-dev-and-release-vs1714p7OfficeDev/microsoft-365-agents-toolkit:copilot/cherry-pick-pr-15719-to-dev-and-release-vs1714p7Copy head branch name to clipboard