### Motivation
Ease the efforts of modifying configurations in automatic workflow and scripts, like Docker and helm chart.
### Modification
Add a `selector` property into `application.yml` to enable switching configuration simply by environment variables or system properties, and filter the unselected options, leaving only selected one.
### Result
- We can switch a configuration by environment variables or system property
- Closes#4511
* Add apdex function to OAL
* Add empty line
* Setup config watcher
* Add identifier type to function parameter
* Add config test
* Update score algorithm
* Replace responseCode with status
* Add comments about apdex score algorithm
* Add docs
* Add e2e test case
* Update test case
* Fix disptch class generating error
* Update value name of apdex metric
* Tuning threshold
* Fix single tolerated point bug
* Provide Consul dynamic configuration center implementation
* Add more unit tests
* Fix unit test
* Add more unit tests and remove unused file
* Remove redundant doc