### 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
* Support dynamic column in the source.
* Support activeExtraModelColumns as a default OFF option.
* Fix words
* Update backend-setup.md
Fix format issue.
* Support grpc exporter.
* Support scope(all) metric export and finish document.
* Close exporter even in local debug env. And fix CI.
* Remove the system.out
* Fix absent 4.
* Support subscription from remote.
* Add the doc
* Update application.yml
* Finish the basic codes of telemetry.
* Add many telemetry in oap.
* Fix a test case.
* Finish all telemetry metric.
* Fix format.
* Make telemetry works.
* Support JVM metrics.
* Add doc for telemetry.
* Fix typo.
* Fix#2135
* Replace v5 changes by a link to 5.x branch. New v6 changelog.
* Finish query doc and fix a missing field in alarm doc.
* Add link to official oal in alarm doc.
* Fix words.
* Fix some doc
* Update README.md
* Update README.md
* Update README.md
* Update README.md