[Release strategy] Alway release 2.0.x and only do bugfix until we could release 2.1.0 base on dev branch

[zhongjiajie]

Currently, the next release version of DS is 2.0.3. but they are a huge gap between branch 2.0.3 and branch dev. This is bad news for our community due to the following reasons:

• Have lots of jobs to do during our release: We need to cherry-pick PRs to <version>-prepare branch, such as [Cherry-pick-2.0.3] 20220107 #7871, TBO, is would cause our so many times on it. What's more, sometimes we have to write the same function code to <version>-prepare and dev due to their a quite different for now. such as [python] Add independent deployment for python gateway server #7549 and [cherry-pick][python] Make dolphinscheduler python API works to 2.0.2 #7608
• Feature or bugfix was already done in dev but release in time: Some features or bugfixs may already be done in branch dev, but we do not cherry-pick to release branch. Users should build by themself if they want to have a try.

So I suggest we should release 2.1.0 base on branch dev ASAP. And before that, we only release 2.0.x which should only do bugfixs based on the previous release, without feature adding.

And then e2e block our releasing process, which you could find in releated https://github.com/apache/dolphinscheduler/issues?q=is%3Aissue+is%3Aopen+label%3A%22e2e%22