Release version 2.21.0

Merge pull request #942 from scouter-project/develop

Develop

Merge pull request #867 from scouter-project/feature/866-exception-on…

…-java17

Feature/866 exception on java17

Merge branch 'master' into develop

Merge pull request #831 from scouter-project/develop

version snapshot

Merge pull request #822 from scouter-project/develop

release v2.15.0

Update Setup_kr.md

snapshot-version