Support to enable CI, CD features independently

[LinuxSuRen]

trafficstars

Some users might only want to use parts of the whole KubeSphere DevOps. For example, @codering mentioned he only want to use the CD feature.

This is not a complex feature request. But we still need to do some work. See the following items:

• [ ] #698
• [ ] #699
• [ ] #700
• [ ] #701

Refs

• https://github.com/kubesphere/ks-devops/issues/583

/kind feature

[codering]

ref https://github.com/kubesphere/ks-installer/pull/2181

[chilianyi]

https://github.com/kubesphere/ks-devops/issues/845