### 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
* [Feature] Officially support ElasticSearch 7 as backend storage
* Extract bootstrap module to be shared by multiple starters
* Add missing configuration file and distinguish different version in test
* Update known-oap-backend-dependencies-es7.txt
Update the dependency lib
* Fix missing adaptation to ElasticSearch 7
* Rename ElasticSearch 7 specific class with Es7 infix
* Fix miss-adapted ElasticSearch DAO API
* Add ES7 specific configuration and polish documentations
* Polish documentations
* Polish documentations
* Is it a typo or not?
* delete datasource-settings.properties
* handle 'metadataQueryMaxSize'
* delete DynamicModuleConfig.java
* modify mysql config
* parsing yaml to support the configuration for multiple properties
* delete datasource-settings.properties
* modify doc
* add properties for docker-entrypoint.sh
* add testLoadConfig()
* The new feature of Elasticsearch storage with the time series implementation.
* Time bucket util improve.
* Fixed some Gramma error.
* Update ttl.md
Polish English a little.
* Update ttl.md
Add more explicit description of TTL
* Update ttl.md
* Update StorageModuleElasticsearchConfig.java
Set otherMetricsDataTTL = 0 as default, make user more clear.
* Rename the timeSeriesAble to capableOfTimeSeries
* Fixed a test case failure.
* Make Jaeger receiver works in 12450 as default.
* Finish compile and codebase.
* Make codes runnable.
* Finish Jaeger query tests.
* Add document for jaeger receiver.
* Add readme.
* Fix a break link.
* Finish doc.
* Codebase for zipkin span persistence.
* Fix missing fields in storage.
* Miss the latency field.
* Finish some tests.
* Fix wrong latency.
* Finish doc and reset application.yml
* Make the description more clear.
* Added elasticsearch warehouse certification support
* Add the elasticsearch service for Http Basic instructions
* Update backend-storage.md
Change document.
* 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