Main (and v1) Branch Protection Rules and PR enforcement

Currently the main branch is not protected, so users with write access can directly push to main and v1. We could enforce to have PRs always (what we anyway do now), but the release action would not be able to do pom.xml version updates directly neither. This is one issue to solve / discuss.

The other part to discuss below this issue is it would be an idea to force approvals from code owners, since this is relatively small team it would not be convenient (think holidays), but with 1 required code owner approval for all PRs could work.

main と v1 のブランチ保護設定を確認し、次に release action とその pom.xml のバージョン更新を調査します。まず、直接のリリース更新を引き続き可能にする必要があるか、また code-owner の承認が必要かを明確にします。合意された保護ポリシーによってリリースが引き続き機能できる状態になれば完了です。