Guide about how to independently use Jenkins config controller

It's possible to independently use [the Jenkins config controller](https://github.com/kubesphere/ks-devops/tree/master/controllers/jenkins/config). It means users can take advantage of the Jenkins config controller to update the configuration of Jenkins via manipulating a ConfigMap. But there are some steps you might need to follow:

* Create a Configmap for the controller
* Necessary information for the Jenkins connection
* Create a ConfigMap for the Jenkins configuration
* Deploy a deployment of the config controller
* Do your tests

## TODO

As I mentioned, this is possible. But before that, we need to do something:

- [x] #274

## References

* https://github.com/kubesphere/ks-devops/tree/master/controllers/jenkinsconfig

Start with controllers/jenkins/config and the referenced controllers/jenkinsconfig path to understand the controller's deployment and ConfigMap inputs. Document the listed setup steps—controller ConfigMap, Jenkins configuration ConfigMap, deployment, and testing—and verify the guide against the completed #274 prerequisite.

Written by the indexing model from the issue text.